vendor/llvm/llvm-r72732

1 files changed, 918 insertions, 0 deletions

diff --git a/lib/Target/X86/README-SSE.txt b/lib/Target/X86/README-SSE.txt
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index 000000000000..71ad51c7984e
--- /dev/null
+++ b/lib/Target/X86/README-SSE.txt
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+//===---------------------------------------------------------------------===//
+// Random ideas for the X86 backend: SSE-specific stuff.
+//===---------------------------------------------------------------------===//
+
+- Consider eliminating the unaligned SSE load intrinsics, replacing them with
+  unaligned LLVM load instructions.
+
+//===---------------------------------------------------------------------===//
+
+Expand libm rounding functions inline:  Significant speedups possible.
+http://gcc.gnu.org/ml/gcc-patches/2006-10/msg00909.html
+
+//===---------------------------------------------------------------------===//
+
+When compiled with unsafemath enabled, "main" should enable SSE DAZ mode and
+other fast SSE modes.
+
+//===---------------------------------------------------------------------===//
+
+Think about doing i64 math in SSE regs on x86-32.
+
+//===---------------------------------------------------------------------===//
+
+This testcase should have no SSE instructions in it, and only one load from
+a constant pool:
+
+double %test3(bool %B) {
+        %C = select bool %B, double 123.412, double 523.01123123
+        ret double %C
+}
+
+Currently, the select is being lowered, which prevents the dag combiner from
+turning 'select (load CPI1), (load CPI2)' -> 'load (select CPI1, CPI2)'
+
+The pattern isel got this one right.
+
+//===---------------------------------------------------------------------===//
+
+SSE doesn't have [mem] op= reg instructions.  If we have an SSE instruction
+like this:
+
+  X += y
+
+and the register allocator decides to spill X, it is cheaper to emit this as:
+
+Y += [xslot]
+store Y -> [xslot]
+
+than as:
+
+tmp = [xslot]
+tmp += y
+store tmp -> [xslot]
+
+..and this uses one fewer register (so this should be done at load folding
+time, not at spiller time).  *Note* however that this can only be done
+if Y is dead.  Here's a testcase:
+
+@.str_3 = external global [15 x i8]
+declare void @printf(i32, ...)
+define void @main() {
+build_tree.exit:
+	br label %no_exit.i7
+
+no_exit.i7:		; preds = %no_exit.i7, %build_tree.exit
+	%tmp.0.1.0.i9 = phi double [ 0.000000e+00, %build_tree.exit ],
+                                   [ %tmp.34.i18, %no_exit.i7 ]
+	%tmp.0.0.0.i10 = phi double [ 0.000000e+00, %build_tree.exit ],
+                                    [ %tmp.28.i16, %no_exit.i7 ]
+	%tmp.28.i16 = add double %tmp.0.0.0.i10, 0.000000e+00
+	%tmp.34.i18 = add double %tmp.0.1.0.i9, 0.000000e+00
+	br i1 false, label %Compute_Tree.exit23, label %no_exit.i7
+
+Compute_Tree.exit23:		; preds = %no_exit.i7
+	tail call void (i32, ...)* @printf( i32 0 )
+	store double %tmp.34.i18, double* null
+	ret void
+}
+
+We currently emit:
+
+.BBmain_1:
+        xorpd %XMM1, %XMM1
+        addsd %XMM0, %XMM1
+***     movsd %XMM2, QWORD PTR [%ESP + 8]
+***     addsd %XMM2, %XMM1
+***     movsd QWORD PTR [%ESP + 8], %XMM2
+        jmp .BBmain_1   # no_exit.i7
+
+This is a bugpoint reduced testcase, which is why the testcase doesn't make
+much sense (e.g. its an infinite loop). :)
+
+//===---------------------------------------------------------------------===//
+
+SSE should implement 'select_cc' using 'emulated conditional moves' that use
+pcmp/pand/pandn/por to do a selection instead of a conditional branch:
+
+double %X(double %Y, double %Z, double %A, double %B) {
+        %C = setlt double %A, %B
+        %z = add double %Z, 0.0    ;; select operand is not a load
+        %D = select bool %C, double %Y, double %z
+        ret double %D
+}
+
+We currently emit:
+
+_X:
+        subl $12, %esp
+        xorpd %xmm0, %xmm0
+        addsd 24(%esp), %xmm0
+        movsd 32(%esp), %xmm1
+        movsd 16(%esp), %xmm2
+        ucomisd 40(%esp), %xmm1
+        jb LBB_X_2
+LBB_X_1:
+        movsd %xmm0, %xmm2
+LBB_X_2:
+        movsd %xmm2, (%esp)
+        fldl (%esp)
+        addl $12, %esp
+        ret
+
+//===---------------------------------------------------------------------===//
+
+It's not clear whether we should use pxor or xorps / xorpd to clear XMM
+registers. The choice may depend on subtarget information. We should do some
+more experiments on different x86 machines.
+
+//===---------------------------------------------------------------------===//
+
+Lower memcpy / memset to a series of SSE 128 bit move instructions when it's
+feasible.
+
+//===---------------------------------------------------------------------===//
+
+Codegen:
+  if (copysign(1.0, x) == copysign(1.0, y))
+into:
+  if (x^y & mask)
+when using SSE.
+
+//===---------------------------------------------------------------------===//
+
+Use movhps to update upper 64-bits of a v4sf value. Also movlps on lower half
+of a v4sf value.
+
+//===---------------------------------------------------------------------===//
+
+Better codegen for vector_shuffles like this { x, 0, 0, 0 } or { x, 0, x, 0}.
+Perhaps use pxor / xorp* to clear a XMM register first?
+
+//===---------------------------------------------------------------------===//
+
+How to decide when to use the "floating point version" of logical ops? Here are
+some code fragments:
+
+	movaps LCPI5_5, %xmm2
+	divps %xmm1, %xmm2
+	mulps %xmm2, %xmm3
+	mulps 8656(%ecx), %xmm3
+	addps 8672(%ecx), %xmm3
+	andps LCPI5_6, %xmm2
+	andps LCPI5_1, %xmm3
+	por %xmm2, %xmm3
+	movdqa %xmm3, (%edi)
+
+	movaps LCPI5_5, %xmm1
+	divps %xmm0, %xmm1
+	mulps %xmm1, %xmm3
+	mulps 8656(%ecx), %xmm3
+	addps 8672(%ecx), %xmm3
+	andps LCPI5_6, %xmm1
+	andps LCPI5_1, %xmm3
+	orps %xmm1, %xmm3
+	movaps %xmm3, 112(%esp)
+	movaps %xmm3, (%ebx)
+
+Due to some minor source change, the later case ended up using orps and movaps
+instead of por and movdqa. Does it matter?
+
+//===---------------------------------------------------------------------===//
+
+X86RegisterInfo::copyRegToReg() returns X86::MOVAPSrr for VR128. Is it possible
+to choose between movaps, movapd, and movdqa based on types of source and
+destination?
+
+How about andps, andpd, and pand? Do we really care about the type of the packed
+elements? If not, why not always use the "ps" variants which are likely to be
+shorter.
+
+//===---------------------------------------------------------------------===//
+
+External test Nurbs exposed some problems. Look for
+__ZN15Nurbs_SSE_Cubic17TessellateSurfaceE, bb cond_next140. This is what icc
+emits:
+
+        movaps    (%edx), %xmm2                                 #59.21
+        movaps    (%edx), %xmm5                                 #60.21
+        movaps    (%edx), %xmm4                                 #61.21
+        movaps    (%edx), %xmm3                                 #62.21
+        movl      40(%ecx), %ebp                                #69.49
+        shufps    $0, %xmm2, %xmm5                              #60.21
+        movl      100(%esp), %ebx                               #69.20
+        movl      (%ebx), %edi                                  #69.20
+        imull     %ebp, %edi                                    #69.49
+        addl      (%eax), %edi                                  #70.33
+        shufps    $85, %xmm2, %xmm4                             #61.21
+        shufps    $170, %xmm2, %xmm3                            #62.21
+        shufps    $255, %xmm2, %xmm2                            #63.21
+        lea       (%ebp,%ebp,2), %ebx                           #69.49
+        negl      %ebx                                          #69.49
+        lea       -3(%edi,%ebx), %ebx                           #70.33
+        shll      $4, %ebx                                      #68.37
+        addl      32(%ecx), %ebx                                #68.37
+        testb     $15, %bl                                      #91.13
+        jne       L_B1.24       # Prob 5%                       #91.13
+
+This is the llvm code after instruction scheduling:
+
+cond_next140 (0xa910740, LLVM BB @0xa90beb0):
+	%reg1078 = MOV32ri -3
+	%reg1079 = ADD32rm %reg1078, %reg1068, 1, %NOREG, 0
+	%reg1037 = MOV32rm %reg1024, 1, %NOREG, 40
+	%reg1080 = IMUL32rr %reg1079, %reg1037
+	%reg1081 = MOV32rm %reg1058, 1, %NOREG, 0
+	%reg1038 = LEA32r %reg1081, 1, %reg1080, -3
+	%reg1036 = MOV32rm %reg1024, 1, %NOREG, 32
+	%reg1082 = SHL32ri %reg1038, 4
+	%reg1039 = ADD32rr %reg1036, %reg1082
+	%reg1083 = MOVAPSrm %reg1059, 1, %NOREG, 0
+	%reg1034 = SHUFPSrr %reg1083, %reg1083, 170
+	%reg1032 = SHUFPSrr %reg1083, %reg1083, 0
+	%reg1035 = SHUFPSrr %reg1083, %reg1083, 255
+	%reg1033 = SHUFPSrr %reg1083, %reg1083, 85
+	%reg1040 = MOV32rr %reg1039
+	%reg1084 = AND32ri8 %reg1039, 15
+	CMP32ri8 %reg1084, 0
+	JE mbb<cond_next204,0xa914d30>
+
+Still ok. After register allocation:
+
+cond_next140 (0xa910740, LLVM BB @0xa90beb0):
+	%EAX = MOV32ri -3
+	%EDX = MOV32rm <fi#3>, 1, %NOREG, 0
+	ADD32rm %EAX<def&use>, %EDX, 1, %NOREG, 0
+	%EDX = MOV32rm <fi#7>, 1, %NOREG, 0
+	%EDX = MOV32rm %EDX, 1, %NOREG, 40
+	IMUL32rr %EAX<def&use>, %EDX
+	%ESI = MOV32rm <fi#5>, 1, %NOREG, 0
+	%ESI = MOV32rm %ESI, 1, %NOREG, 0
+	MOV32mr <fi#4>, 1, %NOREG, 0, %ESI
+	%EAX = LEA32r %ESI, 1, %EAX, -3
+	%ESI = MOV32rm <fi#7>, 1, %NOREG, 0
+	%ESI = MOV32rm %ESI, 1, %NOREG, 32
+	%EDI = MOV32rr %EAX
+	SHL32ri %EDI<def&use>, 4
+	ADD32rr %EDI<def&use>, %ESI
+	%XMM0 = MOVAPSrm %ECX, 1, %NOREG, 0
+	%XMM1 = MOVAPSrr %XMM0
+	SHUFPSrr %XMM1<def&use>, %XMM1, 170
+	%XMM2 = MOVAPSrr %XMM0
+	SHUFPSrr %XMM2<def&use>, %XMM2, 0
+	%XMM3 = MOVAPSrr %XMM0
+	SHUFPSrr %XMM3<def&use>, %XMM3, 255
+	SHUFPSrr %XMM0<def&use>, %XMM0, 85
+	%EBX = MOV32rr %EDI
+	AND32ri8 %EBX<def&use>, 15
+	CMP32ri8 %EBX, 0
+	JE mbb<cond_next204,0xa914d30>
+
+This looks really bad. The problem is shufps is a destructive opcode. Since it
+appears as operand two in more than one shufps ops. It resulted in a number of
+copies. Note icc also suffers from the same problem. Either the instruction
+selector should select pshufd or The register allocator can made the two-address
+to three-address transformation.
+
+It also exposes some other problems. See MOV32ri -3 and the spills.
+
+//===---------------------------------------------------------------------===//
+
+http://gcc.gnu.org/bugzilla/show_bug.cgi?id=25500
+
+LLVM is producing bad code.
+
+LBB_main_4:	# cond_true44
+	addps %xmm1, %xmm2
+	subps %xmm3, %xmm2
+	movaps (%ecx), %xmm4
+	movaps %xmm2, %xmm1
+	addps %xmm4, %xmm1
+	addl $16, %ecx
+	incl %edx
+	cmpl $262144, %edx
+	movaps %xmm3, %xmm2
+	movaps %xmm4, %xmm3
+	jne LBB_main_4	# cond_true44
+
+There are two problems. 1) No need to two loop induction variables. We can
+compare against 262144 * 16. 2) Known register coalescer issue. We should
+be able eliminate one of the movaps:
+
+	addps %xmm2, %xmm1    <=== Commute!
+	subps %xmm3, %xmm1
+	movaps (%ecx), %xmm4
+	movaps %xmm1, %xmm1   <=== Eliminate!
+	addps %xmm4, %xmm1
+	addl $16, %ecx
+	incl %edx
+	cmpl $262144, %edx
+	movaps %xmm3, %xmm2
+	movaps %xmm4, %xmm3
+	jne LBB_main_4	# cond_true44
+
+//===---------------------------------------------------------------------===//
+
+Consider:
+
+__m128 test(float a) {
+  return _mm_set_ps(0.0, 0.0, 0.0, a*a);
+}
+
+This compiles into:
+
+movss 4(%esp), %xmm1
+mulss %xmm1, %xmm1
+xorps %xmm0, %xmm0
+movss %xmm1, %xmm0
+ret
+
+Because mulss doesn't modify the top 3 elements, the top elements of 
+xmm1 are already zero'd.  We could compile this to:
+
+movss 4(%esp), %xmm0
+mulss %xmm0, %xmm0
+ret
+
+//===---------------------------------------------------------------------===//
+
+Here's a sick and twisted idea.  Consider code like this:
+
+__m128 test(__m128 a) {
+  float b = *(float*)&A;
+  ...
+  return _mm_set_ps(0.0, 0.0, 0.0, b);
+}
+
+This might compile to this code:
+
+movaps c(%esp), %xmm1
+xorps %xmm0, %xmm0
+movss %xmm1, %xmm0
+ret
+
+Now consider if the ... code caused xmm1 to get spilled.  This might produce
+this code:
+
+movaps c(%esp), %xmm1
+movaps %xmm1, c2(%esp)
+...
+
+xorps %xmm0, %xmm0
+movaps c2(%esp), %xmm1
+movss %xmm1, %xmm0
+ret
+
+However, since the reload is only used by these instructions, we could 
+"fold" it into the uses, producing something like this:
+
+movaps c(%esp), %xmm1
+movaps %xmm1, c2(%esp)
+...
+
+movss c2(%esp), %xmm0
+ret
+
+... saving two instructions.
+
+The basic idea is that a reload from a spill slot, can, if only one 4-byte 
+chunk is used, bring in 3 zeros the the one element instead of 4 elements.
+This can be used to simplify a variety of shuffle operations, where the
+elements are fixed zeros.
+
+//===---------------------------------------------------------------------===//
+
+__m128d test1( __m128d A, __m128d B) {
+  return _mm_shuffle_pd(A, B, 0x3);
+}
+
+compiles to
+
+shufpd $3, %xmm1, %xmm0
+
+Perhaps it's better to use unpckhpd instead?
+
+unpckhpd %xmm1, %xmm0
+
+Don't know if unpckhpd is faster. But it is shorter.
+
+//===---------------------------------------------------------------------===//
+
+This code generates ugly code, probably due to costs being off or something:
+
+define void @test(float* %P, <4 x float>* %P2 ) {
+        %xFloat0.688 = load float* %P
+        %tmp = load <4 x float>* %P2
+        %inFloat3.713 = insertelement <4 x float> %tmp, float 0.0, i32 3
+        store <4 x float> %inFloat3.713, <4 x float>* %P2
+        ret void
+}
+
+Generates:
+
+_test:
+	movl	8(%esp), %eax
+	movaps	(%eax), %xmm0
+	pxor	%xmm1, %xmm1
+	movaps	%xmm0, %xmm2
+	shufps	$50, %xmm1, %xmm2
+	shufps	$132, %xmm2, %xmm0
+	movaps	%xmm0, (%eax)
+	ret
+
+Would it be better to generate:
+
+_test:
+        movl 8(%esp), %ecx
+        movaps (%ecx), %xmm0
+	xor %eax, %eax
+        pinsrw $6, %eax, %xmm0
+        pinsrw $7, %eax, %xmm0
+        movaps %xmm0, (%ecx)
+        ret
+
+?
+
+//===---------------------------------------------------------------------===//
+
+Some useful information in the Apple Altivec / SSE Migration Guide:
+
+http://developer.apple.com/documentation/Performance/Conceptual/
+Accelerate_sse_migration/index.html
+
+e.g. SSE select using and, andnot, or. Various SSE compare translations.
+
+//===---------------------------------------------------------------------===//
+
+Add hooks to commute some CMPP operations.
+
+//===---------------------------------------------------------------------===//
+
+Apply the same transformation that merged four float into a single 128-bit load
+to loads from constant pool.
+
+//===---------------------------------------------------------------------===//
+
+Floating point max / min are commutable when -enable-unsafe-fp-path is
+specified. We should turn int_x86_sse_max_ss and X86ISD::FMIN etc. into other
+nodes which are selected to max / min instructions that are marked commutable.
+
+//===---------------------------------------------------------------------===//
+
+We should materialize vector constants like "all ones" and "signbit" with 
+code like:
+
+     cmpeqps xmm1, xmm1   ; xmm1 = all-ones
+
+and:
+     cmpeqps xmm1, xmm1   ; xmm1 = all-ones
+     psrlq   xmm1, 31     ; xmm1 = all 100000000000...
+
+instead of using a load from the constant pool.  The later is important for
+ABS/NEG/copysign etc.
+
+//===---------------------------------------------------------------------===//
+
+These functions:
+
+#include <xmmintrin.h>
+__m128i a;
+void x(unsigned short n) {
+  a = _mm_slli_epi32 (a, n);
+}
+void y(unsigned n) {
+  a = _mm_slli_epi32 (a, n);
+}
+
+compile to ( -O3 -static -fomit-frame-pointer):
+_x:
+        movzwl  4(%esp), %eax
+        movd    %eax, %xmm0
+        movaps  _a, %xmm1
+        pslld   %xmm0, %xmm1
+        movaps  %xmm1, _a
+        ret
+_y:
+        movd    4(%esp), %xmm0
+        movaps  _a, %xmm1
+        pslld   %xmm0, %xmm1
+        movaps  %xmm1, _a
+        ret
+
+"y" looks good, but "x" does silly movzwl stuff around into a GPR.  It seems
+like movd would be sufficient in both cases as the value is already zero 
+extended in the 32-bit stack slot IIRC.  For signed short, it should also be
+save, as a really-signed value would be undefined for pslld.
+
+
+//===---------------------------------------------------------------------===//
+
+#include <math.h>
+int t1(double d) { return signbit(d); }
+
+This currently compiles to:
+	subl	$12, %esp
+	movsd	16(%esp), %xmm0
+	movsd	%xmm0, (%esp)
+	movl	4(%esp), %eax
+	shrl	$31, %eax
+	addl	$12, %esp
+	ret
+
+We should use movmskp{s|d} instead.
+
+//===---------------------------------------------------------------------===//
+
+CodeGen/X86/vec_align.ll tests whether we can turn 4 scalar loads into a single
+(aligned) vector load.  This functionality has a couple of problems.
+
+1. The code to infer alignment from loads of globals is in the X86 backend,
+   not the dag combiner.  This is because dagcombine2 needs to be able to see
+   through the X86ISD::Wrapper node, which DAGCombine can't really do.
+2. The code for turning 4 x load into a single vector load is target 
+   independent and should be moved to the dag combiner.
+3. The code for turning 4 x load into a vector load can only handle a direct 
+   load from a global or a direct load from the stack.  It should be generalized
+   to handle any load from P, P+4, P+8, P+12, where P can be anything.
+4. The alignment inference code cannot handle loads from globals in non-static
+   mode because it doesn't look through the extra dyld stub load.  If you try
+   vec_align.ll without -relocation-model=static, you'll see what I mean.
+
+//===---------------------------------------------------------------------===//
+
+We should lower store(fneg(load p), q) into an integer load+xor+store, which
+eliminates a constant pool load.  For example, consider:
+
+define i64 @ccosf(float %z.0, float %z.1) nounwind readonly  {
+entry:
+ %tmp6 = sub float -0.000000e+00, %z.1		; <float> [#uses=1]
+ %tmp20 = tail call i64 @ccoshf( float %tmp6, float %z.0 ) nounwind readonly
+ ret i64 %tmp20
+}
+
+This currently compiles to:
+
+LCPI1_0:					#  <4 x float>
+	.long	2147483648	# float -0
+	.long	2147483648	# float -0
+	.long	2147483648	# float -0
+	.long	2147483648	# float -0
+_ccosf:
+	subl	$12, %esp
+	movss	16(%esp), %xmm0
+	movss	%xmm0, 4(%esp)
+	movss	20(%esp), %xmm0
+	xorps	LCPI1_0, %xmm0
+	movss	%xmm0, (%esp)
+	call	L_ccoshf$stub
+	addl	$12, %esp
+	ret
+
+Note the load into xmm0, then xor (to negate), then store.  In PIC mode,
+this code computes the pic base and does two loads to do the constant pool 
+load, so the improvement is much bigger.
+
+The tricky part about this xform is that the argument load/store isn't exposed
+until post-legalize, and at that point, the fneg has been custom expanded into 
+an X86 fxor.  This means that we need to handle this case in the x86 backend
+instead of in target independent code.
+
+//===---------------------------------------------------------------------===//
+
+Non-SSE4 insert into 16 x i8 is atrociously bad.
+
+//===---------------------------------------------------------------------===//
+
+<2 x i64> extract is substantially worse than <2 x f64>, even if the destination
+is memory.
+
+//===---------------------------------------------------------------------===//
+
+SSE4 extract-to-mem ops aren't being pattern matched because of the AssertZext
+sitting between the truncate and the extract.
+
+//===---------------------------------------------------------------------===//
+
+INSERTPS can match any insert (extract, imm1), imm2 for 4 x float, and insert
+any number of 0.0 simultaneously.  Currently we only use it for simple
+insertions.
+
+See comments in LowerINSERT_VECTOR_ELT_SSE4.
+
+//===---------------------------------------------------------------------===//
+
+On a random note, SSE2 should declare insert/extract of 2 x f64 as legal, not
+Custom.  All combinations of insert/extract reg-reg, reg-mem, and mem-reg are
+legal, it'll just take a few extra patterns written in the .td file.
+
+Note: this is not a code quality issue; the custom lowered code happens to be
+right, but we shouldn't have to custom lower anything.  This is probably related
+to <2 x i64> ops being so bad.
+
+//===---------------------------------------------------------------------===//
+
+'select' on vectors and scalars could be a whole lot better.  We currently 
+lower them to conditional branches.  On x86-64 for example, we compile this:
+
+double test(double a, double b, double c, double d) { return a<b ? c : d; }
+
+to:
+
+_test:
+	ucomisd	%xmm0, %xmm1
+	ja	LBB1_2	# entry
+LBB1_1:	# entry
+	movapd	%xmm3, %xmm2
+LBB1_2:	# entry
+	movapd	%xmm2, %xmm0
+	ret
+
+instead of:
+
+_test:
+	cmpltsd	%xmm1, %xmm0
+	andpd	%xmm0, %xmm2
+	andnpd	%xmm3, %xmm0
+	orpd	%xmm2, %xmm0
+	ret
+
+For unpredictable branches, the later is much more efficient.  This should
+just be a matter of having scalar sse map to SELECT_CC and custom expanding
+or iseling it.
+
+//===---------------------------------------------------------------------===//
+
+LLVM currently generates stack realignment code, when it is not necessary
+needed. The problem is that we need to know about stack alignment too early,
+before RA runs.
+
+At that point we don't know, whether there will be vector spill, or not.
+Stack realignment logic is overly conservative here, but otherwise we can
+produce unaligned loads/stores.
+
+Fixing this will require some huge RA changes.
+
+Testcase:
+#include <emmintrin.h>
+
+typedef short vSInt16 __attribute__ ((__vector_size__ (16)));
+
+static const vSInt16 a = {- 22725, - 12873, - 22725, - 12873, - 22725, - 12873,
+- 22725, - 12873};;
+
+vSInt16 madd(vSInt16 b)
+{
+    return _mm_madd_epi16(a, b);
+}
+
+Generated code (x86-32, linux):
+madd:
+        pushl   %ebp
+        movl    %esp, %ebp
+        andl    $-16, %esp
+        movaps  .LCPI1_0, %xmm1
+        pmaddwd %xmm1, %xmm0
+        movl    %ebp, %esp
+        popl    %ebp
+        ret
+
+//===---------------------------------------------------------------------===//
+
+Consider:
+#include <emmintrin.h> 
+__m128 foo2 (float x) {
+ return _mm_set_ps (0, 0, x, 0);
+}
+
+In x86-32 mode, we generate this spiffy code:
+
+_foo2:
+	movss	4(%esp), %xmm0
+	pshufd	$81, %xmm0, %xmm0
+	ret
+
+in x86-64 mode, we generate this code, which could be better:
+
+_foo2:
+	xorps	%xmm1, %xmm1
+	movss	%xmm0, %xmm1
+	pshufd	$81, %xmm1, %xmm0
+	ret
+
+In sse4 mode, we could use insertps to make both better.
+
+Here's another testcase that could use insertps [mem]:
+
+#include <xmmintrin.h>
+extern float x2, x3;
+__m128 foo1 (float x1, float x4) {
+ return _mm_set_ps (x2, x1, x3, x4);
+}
+
+gcc mainline compiles it to:
+
+foo1:
+       insertps        $0x10, x2(%rip), %xmm0
+       insertps        $0x10, x3(%rip), %xmm1
+       movaps  %xmm1, %xmm2
+       movlhps %xmm0, %xmm2
+       movaps  %xmm2, %xmm0
+       ret
+
+//===---------------------------------------------------------------------===//
+
+We compile vector multiply-by-constant into poor code:
+
+define <4 x i32> @f(<4 x i32> %i) nounwind  {
+	%A = mul <4 x i32> %i, < i32 10, i32 10, i32 10, i32 10 >
+	ret <4 x i32> %A
+}
+
+On targets without SSE4.1, this compiles into:
+
+LCPI1_0:					##  <4 x i32>
+	.long	10
+	.long	10
+	.long	10
+	.long	10
+	.text
+	.align	4,0x90
+	.globl	_f
+_f:
+	pshufd	$3, %xmm0, %xmm1
+	movd	%xmm1, %eax
+	imull	LCPI1_0+12, %eax
+	movd	%eax, %xmm1
+	pshufd	$1, %xmm0, %xmm2
+	movd	%xmm2, %eax
+	imull	LCPI1_0+4, %eax
+	movd	%eax, %xmm2
+	punpckldq	%xmm1, %xmm2
+	movd	%xmm0, %eax
+	imull	LCPI1_0, %eax
+	movd	%eax, %xmm1
+	movhlps	%xmm0, %xmm0
+	movd	%xmm0, %eax
+	imull	LCPI1_0+8, %eax
+	movd	%eax, %xmm0
+	punpckldq	%xmm0, %xmm1
+	movaps	%xmm1, %xmm0
+	punpckldq	%xmm2, %xmm0
+	ret
+
+It would be better to synthesize integer vector multiplication by constants
+using shifts and adds, pslld and paddd here. And even on targets with SSE4.1,
+simple cases such as multiplication by powers of two would be better as
+vector shifts than as multiplications.
+
+//===---------------------------------------------------------------------===//
+
+We compile this:
+
+__m128i
+foo2 (char x)
+{
+  return _mm_set_epi8 (1, 0, 0, 0, 0, 0, 0, 0, 0, x, 0, 1, 0, 0, 0, 0);
+}
+
+into:
+	movl	$1, %eax
+	xorps	%xmm0, %xmm0
+	pinsrw	$2, %eax, %xmm0
+	movzbl	4(%esp), %eax
+	pinsrw	$3, %eax, %xmm0
+	movl	$256, %eax
+	pinsrw	$7, %eax, %xmm0
+	ret
+
+
+gcc-4.2:
+	subl	$12, %esp
+	movzbl	16(%esp), %eax
+	movdqa	LC0, %xmm0
+	pinsrw	$3, %eax, %xmm0
+	addl	$12, %esp
+	ret
+	.const
+	.align 4
+LC0:
+	.word	0
+	.word	0
+	.word	1
+	.word	0
+	.word	0
+	.word	0
+	.word	0
+	.word	256
+
+With SSE4, it should be
+      movdqa  .LC0(%rip), %xmm0
+      pinsrb  $6, %edi, %xmm0
+
+//===---------------------------------------------------------------------===//
+
+We should transform a shuffle of two vectors of constants into a single vector
+of constants. Also, insertelement of a constant into a vector of constants
+should also result in a vector of constants. e.g. 2008-06-25-VecISelBug.ll.
+
+We compiled it to something horrible:
+
+	.align	4
+LCPI1_1:					##  float
+	.long	1065353216	## float 1
+	.const
+
+	.align	4
+LCPI1_0:					##  <4 x float>
+	.space	4
+	.long	1065353216	## float 1
+	.space	4
+	.long	1065353216	## float 1
+	.text
+	.align	4,0x90
+	.globl	_t
+_t:
+	xorps	%xmm0, %xmm0
+	movhps	LCPI1_0, %xmm0
+	movss	LCPI1_1, %xmm1
+	movaps	%xmm0, %xmm2
+	shufps	$2, %xmm1, %xmm2
+	shufps	$132, %xmm2, %xmm0
+	movaps	%xmm0, 0
+
+//===---------------------------------------------------------------------===//
+rdar://5907648
+
+This function:
+
+float foo(unsigned char x) {
+  return x;
+}
+
+compiles to (x86-32):
+
+define float @foo(i8 zeroext  %x) nounwind  {
+	%tmp12 = uitofp i8 %x to float		; <float> [#uses=1]
+	ret float %tmp12
+}
+
+compiles to:
+
+_foo:
+	subl	$4, %esp
+	movzbl	8(%esp), %eax
+	cvtsi2ss	%eax, %xmm0
+	movss	%xmm0, (%esp)
+	flds	(%esp)
+	addl	$4, %esp
+	ret
+
+We should be able to use:
+  cvtsi2ss 8($esp), %xmm0
+since we know the stack slot is already zext'd.
+
+//===---------------------------------------------------------------------===//
+
+Consider using movlps instead of movsd to implement (scalar_to_vector (loadf64))
+when code size is critical. movlps is slower than movsd on core2 but it's one
+byte shorter.
+
+//===---------------------------------------------------------------------===//
+
+We should use a dynamic programming based approach to tell when using FPStack
+operations is cheaper than SSE.  SciMark montecarlo contains code like this
+for example:
+
+double MonteCarlo_num_flops(int Num_samples) {
+    return ((double) Num_samples)* 4.0;
+}
+
+In fpstack mode, this compiles into:
+
+LCPI1_0:					
+	.long	1082130432	## float 4.000000e+00
+_MonteCarlo_num_flops:
+	subl	$4, %esp
+	movl	8(%esp), %eax
+	movl	%eax, (%esp)
+	fildl	(%esp)
+	fmuls	LCPI1_0
+	addl	$4, %esp
+	ret
+        
+in SSE mode, it compiles into significantly slower code:
+
+_MonteCarlo_num_flops:
+	subl	$12, %esp
+	cvtsi2sd	16(%esp), %xmm0
+	mulsd	LCPI1_0, %xmm0
+	movsd	%xmm0, (%esp)
+	fldl	(%esp)
+	addl	$12, %esp
+	ret
+
+There are also other cases in scimark where using fpstack is better, it is
+cheaper to do fld1 than load from a constant pool for example, so
+"load, add 1.0, store" is better done in the fp stack, etc.
+
+//===---------------------------------------------------------------------===//