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[FastISel][X86] Only fold the cmp into the select when both instructions are in the same basic block. 

If the cmp is in a different basic block, then it is possible that not all
operands of that compare have defined registers. This can happen when one of
the operands to the cmp is a load and the load gets folded into the cmp. In
this case FastISel will skip the load instruction and the vreg is never
defined.

llvm-svn: 211730
This commit is contained in:
Juergen Ributzka 2014-06-25 20:06:12 +00:00
parent cfcd7914da
commit 296833cde9
2 changed files with 65 additions and 5 deletions
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20
llvm/lib/Target/X86/X86FastISel.cpp
View File

@ -1754,8 +1754,11 @@ bool X86FastISel::X86FastEmitCMoveSelect(const Instruction *I) {
const TargetRegisterClass *RC = TLI.getRegClassFor(RetVT);
bool NeedTest = true;
// Optimize conditons coming from a compare.
if (const auto *CI = dyn_cast<CmpInst>(Cond)) {
// Optimize conditons coming from a compare if both instructions are in the
// same basic block (values defined in other basic blocks may not have
// initialized registers).
const auto *CI = dyn_cast<CmpInst>(Cond);
if (CI && (CI->getParent() == I->getParent())) {
CmpInst::Predicate Predicate = optimizeCmpPredicate(CI);
// FCMP_OEQ and FCMP_UNE cannot be checked with a single instruction.
@ -1927,8 +1930,11 @@ bool X86FastISel::X86FastEmitSSESelect(const Instruction *I) {
if (!isTypeLegal(I->getType(), RetVT))
return false;
// Optimize conditons coming from a compare if both instructions are in the
// same basic block (values defined in other basic blocks may not have
// initialized registers).
const auto *CI = dyn_cast<FCmpInst>(I->getOperand(0));
if (!CI)
if (!CI || (CI->getParent() != I->getParent()))
return false;
if (I->getType() != CI->getOperand(0)->getType() ||
@ -2023,8 +2029,12 @@ bool X86FastISel::X86FastEmitPseudoSelect(const Instruction *I) {
const Value *Cond = I->getOperand(0);
X86::CondCode CC = X86::COND_NE;
// Don't emit a test if the condition comes from a compare.
if (const auto *CI = dyn_cast<CmpInst>(Cond)) {
// Optimize conditons coming from a compare if both instructions are in the
// same basic block (values defined in other basic blocks may not have
// initialized registers).
const auto *CI = dyn_cast<CmpInst>(Cond);
if (CI && (CI->getParent() == I->getParent())) {
bool NeedSwap;
std::tie(CC, NeedSwap) = getX86ConditonCode(CI->getPredicate());
if (CC > X86::LAST_VALID_COND)

50
llvm/test/CodeGen/X86/fast-isel-select-cmp.ll Normal file
View File

@ -0,0 +1,50 @@
; RUN: llc < %s -O0 -mtriple=x86_64-apple-darwin10 | FileCheck %s
; Test if we do not fold the cmp into select if the instructions are in
; different basic blocks.
define i32 @select_cmp_cmov_i32(i32 %a, i32 %b) {
; CHECK-LABEL: select_cmp_cmov_i32
; CHECK-LABEL: continue
; CHECK-NOT: cmp
%1 = icmp ult i32 %a, %b
br i1 %1, label %continue, label %exit
continue:
%2 = select i1 %1, i32 %a, i32 %b
ret i32 %2
exit:
ret i32 -1
}
define float @select_fcmp_oeq_f32(float %a, float %b, float %c, float %d) {
; CHECK-LABEL: select_fcmp_oeq_f32
; CHECK-LABEL: continue
; CHECK-NOT: cmp
%1 = fcmp oeq float %a, %b
br i1 %1, label %continue, label %exit
continue:
%2 = select i1 %1, float %c, float %d
ret float %2
exit:
ret float -1.0
}
define float @select_fcmp_one_f32(float %a, float %b, float %c, float %d) {
; CHECK-LABEL: select_fcmp_one_f32
; CHECK-LABEL: continue
; CHECK-NOT: ucomi
%1 = fcmp one float %a, %b
br i1 %1, label %continue, label %exit
continue:
%2 = select i1 %1, float %c, float %d
ret float %2
exit:
ret float -1.0
}