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Not all targets have efficient ISel code generation for select instructions.

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For example, the ARM target does not have efficient ISel handling for vector
selects with scalar conditions. This patch adds a TLI hook which allows the
different targets to report which selects are supported well and which selects
should be converted to CF duting codegen prepare.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@163093 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nadav Rotem
2012-09-02 12:10:19 +00:00
parent 7de7078933
commit 9f40cb32ac
4 changed files with 39 additions and 10 deletions
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29
lib/Transforms/Scalar/CodeGenPrepare.cpp
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@@ -1174,16 +1174,31 @@ static bool isFormingBranchFromSelectProfitable(SelectInst *SI) {
}
/// If we have a SelectInst that will likely profit from branch prediction,
/// turn it into a branch.
bool CodeGenPrepare::OptimizeSelectInst(SelectInst *SI) {
// If we have a SelectInst that will likely profit from branch prediction,
// turn it into a branch.
if (DisableSelectToBranch || OptSize || !TLI ||
!TLI->isPredictableSelectExpensive())
bool VectorCond = !SI->getCondition()->getType()->isIntegerTy(1);
// Can we convert the 'select' to CF ?
if (DisableSelectToBranch || OptSize || !TLI || VectorCond)
return false;
if (!SI->getCondition()->getType()->isIntegerTy(1) ||
!isFormingBranchFromSelectProfitable(SI))
return false;
TargetLowering::SelectSupportKind SelectKind;
if (VectorCond)
SelectKind = TargetLowering::VectorMaskSelect;
else if (SI->getType()->isVectorTy())
SelectKind = TargetLowering::ScalarCondVectorVal;
else
SelectKind = TargetLowering::ScalarValSelect;
// Do we have efficient codegen support for this kind of 'selects' ?
if (TLI->isSelectSupported(SelectKind)) {
// We have efficient codegen support for the select instruction.
// Check if it is profitable to keep this 'select'.
if (!TLI->isPredictableSelectExpensive() ||
!isFormingBranchFromSelectProfitable(SI))
return false;
}
ModifiedDT = true;