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[ValueTracking] readnone CallInsts are fair game for speculation

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Any call which is side effect free is trivially OK to speculate.  We
already had similar logic in EarlyCSE and GVN but we were missing it
from isSafeToSpeculativelyExecute.

This fixes PR24601.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@246232 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Majnemer 2015-08-27 23:03:01 +00:00
parent ef38201ab0
commit 2cdf5c3e03
2 changed files with 21 additions and 39 deletions
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42
lib/Analysis/ValueTracking.cpp
View File

@ -3147,46 +3147,10 @@ bool llvm::isSafeToSpeculativelyExecute(const Value *V,
LI->getPointerOperand(), LI->getAlignment(), DL, CtxI, DT, TLI);
}
case Instruction::Call: {
if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(Inst)) {
switch (II->getIntrinsicID()) {
// These synthetic intrinsics have no side-effects and just mark
// information about their operands.
// FIXME: There are other no-op synthetic instructions that potentially
// should be considered at least *safe* to speculate...
case Intrinsic::dbg_declare:
case Intrinsic::dbg_value:
return true;
case Intrinsic::bswap:
case Intrinsic::ctlz:
case Intrinsic::ctpop:
case Intrinsic::cttz:
case Intrinsic::objectsize:
case Intrinsic::sadd_with_overflow:
case Intrinsic::smul_with_overflow:
case Intrinsic::ssub_with_overflow:
case Intrinsic::uadd_with_overflow:
case Intrinsic::umul_with_overflow:
case Intrinsic::usub_with_overflow:
return true;
// Sqrt should be OK, since the llvm sqrt intrinsic isn't defined to set
// errno like libm sqrt would.
case Intrinsic::sqrt:
case Intrinsic::fma:
case Intrinsic::fmuladd:
case Intrinsic::fabs:
case Intrinsic::minnum:
case Intrinsic::maxnum:
return true;
// TODO: some fp intrinsics are marked as having the same error handling
// as libm. They're safe to speculate when they won't error.
// TODO: are convert_{from,to}_fp16 safe?
// TODO: can we list target-specific intrinsics here?
default: break;
}
}
if (cast<CallInst>(Inst)->doesNotAccessMemory())
return true;
return false; // The called function could have undefined behavior or
// side-effects, even if marked readnone nounwind.
// side-effects.
}
case Instruction::VAArg:
case Instruction::Alloca:

18
test/Transforms/SimplifyCFG/speculate-math.ll
View File

@ -6,6 +6,7 @@ declare float @llvm.fmuladd.f32(float, float, float) nounwind readonly
declare float @llvm.fabs.f32(float) nounwind readonly
declare float @llvm.minnum.f32(float, float) nounwind readonly
declare float @llvm.maxnum.f32(float, float) nounwind readonly
declare float @llvm.copysign.f32(float, float) nounwind readonly
; CHECK-LABEL: @sqrt_test(
; CHECK: select
@ -108,3 +109,20 @@ test_maxnum.exit: ; preds = %cond.else.i, %ent
store float %cond.i, float addrspace(1)* %out, align 4
ret void
}
; CHECK-LABEL: @copysign_test(
; CHECK: select
define void @copysign_test(float addrspace(1)* noalias nocapture %out, float %a, float %b) nounwind {
entry:
%cmp.i = fcmp olt float %a, 0.000000e+00
br i1 %cmp.i, label %test_copysign.exit, label %cond.else.i
cond.else.i: ; preds = %entry
%0 = tail call float @llvm.copysign.f32(float %a, float %b) nounwind readnone
br label %test_copysign.exit
test_copysign.exit: ; preds = %cond.else.i, %entry
%cond.i = phi float [ %0, %cond.else.i ], [ 0x7FF8000000000000, %entry ]
store float %cond.i, float addrspace(1)* %out, align 4
ret void
}