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InstCombine/AMDGPU: Fix constant folding of llvm.amdgcn.{icmp,fcmp}

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Summary:
The return value of these intrinsics should always have 0 bits for
inactive threads. This means that when all arguments are constant
and the comparison evaluates to true, the intrinsic should return
the current exec mask.

Fixes some GL_ARB_shader_ballot tests.

Reviewers: arsenm

Subscribers: kzhuravl, wdng, yaxunl, dstuttard, tpr, llvm-commits, t-tye

Differential Revision: https://reviews.llvm.org/D32344

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@301195 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nicolai Haehnle 2017-04-24 17:08:43 +00:00
parent 8978f2978f
commit 7b717b6e43
2 changed files with 24 additions and 4 deletions
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22
lib/Transforms/InstCombine/InstCombineCalls.cpp
View File

@ -3432,8 +3432,26 @@ Instruction *InstCombiner::visitCallInst(CallInst &CI) {
if (auto *CSrc0 = dyn_cast<Constant>(Src0)) {
if (auto *CSrc1 = dyn_cast<Constant>(Src1)) {
Constant *CCmp = ConstantExpr::getCompare(CCVal, CSrc0, CSrc1);
return replaceInstUsesWith(*II,
ConstantExpr::getSExt(CCmp, II->getType()));
if (CCmp->isNullValue()) {
return replaceInstUsesWith(
*II, ConstantExpr::getSExt(CCmp, II->getType()));
}
// The result of V_ICMP/V_FCMP assembly instructions (which this
// intrinsic exposes) is one bit per thread, masked with the EXEC
// register (which contains the bitmask of live threads). So a
// comparison that always returns true is the same as a read of the
// EXEC register.
Value *NewF = Intrinsic::getDeclaration(
II->getModule(), Intrinsic::read_register, II->getType());
Metadata *MDArgs[] = {MDString::get(II->getContext(), "exec")};
MDNode *MD = MDNode::get(II->getContext(), MDArgs);
Value *Args[] = {MetadataAsValue::get(II->getContext(), MD)};
CallInst *NewCall = Builder->CreateCall(NewF, Args);
NewCall->addAttribute(AttributeList::FunctionIndex,
Attribute::Convergent);
NewCall->takeName(II);
return replaceInstUsesWith(*II, NewCall);
}
// Canonicalize constants to RHS.

6
test/Transforms/InstCombine/amdgcn-intrinsics.ll
View File

@ -1259,7 +1259,7 @@ define i64 @icmp_constant_inputs_false() {
}
; CHECK-LABEL: @icmp_constant_inputs_true(
; CHECK: ret i64 -1
; CHECK: %result = call i64 @llvm.read_register.i64(metadata !0) #4
define i64 @icmp_constant_inputs_true() {
%result = call i64 @llvm.amdgcn.icmp.i32(i32 9, i32 8, i32 34)
ret i64 %result
@ -1524,7 +1524,7 @@ define i64 @fcmp_constant_inputs_false() {
}
; CHECK-LABEL: @fcmp_constant_inputs_true(
; CHECK: ret i64 -1
; CHECK: %result = call i64 @llvm.read_register.i64(metadata !0) #4
define i64 @fcmp_constant_inputs_true() {
%result = call i64 @llvm.amdgcn.fcmp.f32(float 2.0, float 4.0, i32 4)
ret i64 %result
@ -1536,3 +1536,5 @@ define i64 @fcmp_constant_to_rhs_olt(float %x) {
%result = call i64 @llvm.amdgcn.fcmp.f32(float 4.0, float %x, i32 4)
ret i64 %result
}
; CHECK: attributes #4 = { convergent }