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[InstCombine] Remove transformation on call instruction where return value need void to non-void conversion #98536

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merged 6 commits into from
Aug 2, 2024
Merged

[InstCombine] Remove transformation on call instruction where return value need void to non-void conversion #98536

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03bb6f3
[InstCombine] Add an option to not take advantage of void to non-void…
yozhu Jul 11, 2024
0ac5dd8
Add a test case
yozhu Jul 15, 2024
2a4d481
[instcombine] Remove transformation involving return value from call …
yozhu Aug 1, 2024
e61904e
address review feedback
yozhu Aug 1, 2024
0863610
address review feedback 2
yozhu Aug 2, 2024
94d4332
Forgot to remove the unnecessary add instr from the new test case
yozhu Aug 2, 2024
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26 changes: 9 additions & 17 deletions llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4071,9 +4071,7 @@ bool InstCombinerImpl::transformConstExprCastCall(CallBase &Call) {
if (Callee->isDeclaration())
return false; // Cannot transform this return value.

if (!Caller->use_empty() &&
// void -> non-void is handled specially
!NewRetTy->isVoidTy())
if (!Caller->use_empty())
return false; // Cannot transform this return value.
}

Expand Down Expand Up @@ -4233,9 +4231,6 @@ bool InstCombinerImpl::transformConstExprCastCall(CallBase &Call) {

AttributeSet FnAttrs = CallerPAL.getFnAttrs();

if (NewRetTy->isVoidTy())
Caller->setName(""); // Void type should not have a name.
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I think this bit might still be needed? Can you please add another function to your test that does %res = call i32 @foo() but does not use the result? Just want to make sure this doesn't hit some void name assertion.

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Yes this would necessary now after we have tightened the condition above to skip transformation only when return value has uses.


assert((ArgAttrs.size() == FT->getNumParams() || FT->isVarArg()) &&
"missing argument attributes");
AttributeList NewCallerPAL = AttributeList::get(
Expand Down Expand Up @@ -4264,17 +4259,14 @@ bool InstCombinerImpl::transformConstExprCastCall(CallBase &Call) {
Instruction *NC = NewCall;
Value *NV = NC;
if (OldRetTy != NV->getType() && !Caller->use_empty()) {
if (!NV->getType()->isVoidTy()) {
NV = NC = CastInst::CreateBitOrPointerCast(NC, OldRetTy);
NC->setDebugLoc(Caller->getDebugLoc());

auto OptInsertPt = NewCall->getInsertionPointAfterDef();
assert(OptInsertPt && "No place to insert cast");
InsertNewInstBefore(NC, *OptInsertPt);
Worklist.pushUsersToWorkList(*Caller);
} else {
NV = PoisonValue::get(Caller->getType());
}
assert(!NV->getType()->isVoidTy());
NV = NC = CastInst::CreateBitOrPointerCast(NC, OldRetTy);
NC->setDebugLoc(Caller->getDebugLoc());

auto OptInsertPt = NewCall->getInsertionPointAfterDef();
assert(OptInsertPt && "No place to insert cast");
InsertNewInstBefore(NC, *OptInsertPt);
Worklist.pushUsersToWorkList(*Caller);
}

if (!Caller->use_empty())
Expand Down
24 changes: 24 additions & 0 deletions llvm/test/Transforms/InstCombine/skip-opt-void-to-non-void-conversion.ll
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@@ -0,0 +1,24 @@
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
; RUN: opt --passes=instcombine -S < %s | FileCheck %s

define dso_local void @foo() {
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Drop dso_local.

; CHECK-LABEL: define dso_local void @foo() {
; CHECK-NEXT: [[ENTRY:.*:]]
; CHECK-NEXT: ret void
;
entry:
ret void
}

define dso_local i32 @bar() {
; CHECK-LABEL: define dso_local i32 @bar() {
; CHECK-NEXT: [[ENTRY:.*:]]
; CHECK-NEXT: [[TMP0:%.*]] = tail call i32 @foo()
; CHECK-NEXT: [[TMP1:%.*]] = add i32 [[TMP0]], 1
; CHECK-NEXT: ret i32 [[TMP1]]
;
entry:
%1 = tail call i32 @foo()
%2 = add i32 %1, 1
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Can drop the add too :)

ret i32 %2
}
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