vendor/llvm-project/llvmorg-11-init-20887-g2e10b7a39b9vendor/llvm-project/master

1 files changed, 7 insertions, 6 deletions

diff --git a/llvm/lib/Target/X86/X86CmovConversion.cpp b/llvm/lib/Target/X86/X86CmovConversion.cpp
index fe43bf4cbbce1..fe5cb3ae2bf64 100644
--- a/llvm/lib/Target/X86/X86CmovConversion.cpp
+++ b/llvm/lib/Target/X86/X86CmovConversion.cpp
@@ -364,12 +364,13 @@ bool X86CmovConverterPass::collectCmovCandidates(
 /// \param TrueOpDepth depth cost of CMOV true value operand.
 /// \param FalseOpDepth depth cost of CMOV false value operand.
 static unsigned getDepthOfOptCmov(unsigned TrueOpDepth, unsigned FalseOpDepth) {
-  //===--------------------------------------------------------------------===//
-  // With no info about branch weight, we assume 50% for each value operand.
-  // Thus, depth of optimized CMOV instruction is the rounded up average of
-  // its True-Operand-Value-Depth and False-Operand-Value-Depth.
-  //===--------------------------------------------------------------------===//
-  return (TrueOpDepth + FalseOpDepth + 1) / 2;
+  // The depth of the result after branch conversion is
+  // TrueOpDepth * TrueOpProbability + FalseOpDepth * FalseOpProbability.
+  // As we have no info about branch weight, we assume 75% for one and 25% for
+  // the other, and pick the result with the largest resulting depth.
+  return std::max(
+      divideCeil(TrueOpDepth * 3 + FalseOpDepth, 4),
+      divideCeil(FalseOpDepth * 3 + TrueOpDepth, 4));
 }
 
 bool X86CmovConverterPass::checkForProfitableCmovCandidates(