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Automerge: [InstCombine] Simplify with.overflow intrinsics with assum…
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…ption information (#84016)

This patch recognizes never-overflow assumptions generated by rustc to
improve the codegen.
Please refer to rust-lang/hashbrown#509 for
more details.

Closes rust-lang/hashbrown#509
Closes llvm/llvm-project#80637
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@dtcxzyw @github-actions
dtcxzyw authored and github-actions[bot] committed Jan 10, 2025
2 parents 51fd0b0 + 2adcec7 commit 7498bdc
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Showing 2 changed files with 122 additions and 5 deletions.
29 changes: 29 additions & 0 deletions llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -839,6 +839,35 @@ InstCombinerImpl::foldIntrinsicWithOverflowCommon(IntrinsicInst *II) {
if (OptimizeOverflowCheck(WO->getBinaryOp(), WO->isSigned(), WO->getLHS(),
WO->getRHS(), *WO, OperationResult, OverflowResult))
return createOverflowTuple(WO, OperationResult, OverflowResult);

// See whether we can optimize the overflow check with assumption information.
for (User *U : WO->users()) {
if (!match(U, m_ExtractValue<1>(m_Value())))
continue;

for (auto &AssumeVH : AC.assumptionsFor(U)) {
if (!AssumeVH)
continue;
CallInst *I = cast<CallInst>(AssumeVH);
if (!match(I->getArgOperand(0), m_Not(m_Specific(U))))
continue;
if (!isValidAssumeForContext(I, II, /*DT=*/nullptr,
/*AllowEphemerals=*/true))
continue;
Value *Result =
Builder.CreateBinOp(WO->getBinaryOp(), WO->getLHS(), WO->getRHS());
Result->takeName(WO);
if (auto *Inst = dyn_cast<Instruction>(Result)) {
if (WO->isSigned())
Inst->setHasNoSignedWrap();
else
Inst->setHasNoUnsignedWrap();
}
return createOverflowTuple(WO, Result,
ConstantInt::getFalse(U->getType()));
}
}

return nullptr;
}

Expand Down
98 changes: 93 additions & 5 deletions llvm/test/Transforms/InstCombine/overflow.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -11,7 +11,7 @@ define i32 @test1(i32 %a, i32 %b) nounwind ssp {
; CHECK-NEXT: [[TMP0:%.*]] = extractvalue { i32, i1 } [[SADD]], 1
; CHECK-NEXT: br i1 [[TMP0]], label [[IF_THEN:%.*]], label [[IF_END:%.*]]
; CHECK: if.then:
; CHECK-NEXT: tail call void @throwAnExceptionOrWhatever() #[[ATTR2:[0-9]+]]
; CHECK-NEXT: tail call void @throwAnExceptionOrWhatever() #[[ATTR3:[0-9]+]]
; CHECK-NEXT: br label [[IF_END]]
; CHECK: if.end:
; CHECK-NEXT: [[SADD_RESULT:%.*]] = extractvalue { i32, i1 } [[SADD]], 0
Expand Down Expand Up @@ -49,7 +49,7 @@ define i32 @test2(i32 %a, i32 %b, ptr %P) nounwind ssp {
; CHECK-NEXT: [[TMP0:%.*]] = icmp ugt i64 [[ADD_OFF]], 4294967295
; CHECK-NEXT: br i1 [[TMP0]], label [[IF_THEN:%.*]], label [[IF_END:%.*]]
; CHECK: if.then:
; CHECK-NEXT: tail call void @throwAnExceptionOrWhatever() #[[ATTR2]]
; CHECK-NEXT: tail call void @throwAnExceptionOrWhatever() #[[ATTR3]]
; CHECK-NEXT: br label [[IF_END]]
; CHECK: if.end:
; CHECK-NEXT: [[CONV9:%.*]] = trunc i64 [[ADD]] to i32
Expand Down Expand Up @@ -86,7 +86,7 @@ define i64 @test3(i32 %a, i32 %b) nounwind ssp {
; CHECK-NEXT: [[TMP1:%.*]] = icmp ult i64 [[TMP0]], -4294967296
; CHECK-NEXT: br i1 [[TMP1]], label [[IF_THEN:%.*]], label [[IF_END:%.*]]
; CHECK: if.then:
; CHECK-NEXT: tail call void @throwAnExceptionOrWhatever() #[[ATTR2]]
; CHECK-NEXT: tail call void @throwAnExceptionOrWhatever() #[[ATTR3]]
; CHECK-NEXT: br label [[IF_END]]
; CHECK: if.end:
; CHECK-NEXT: ret i64 [[ADD]]
Expand Down Expand Up @@ -116,7 +116,7 @@ define zeroext i8 @test4(i8 signext %a, i8 signext %b) nounwind ssp {
; CHECK-NEXT: [[CMP:%.*]] = extractvalue { i8, i1 } [[SADD]], 1
; CHECK-NEXT: br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_END:%.*]]
; CHECK: if.then:
; CHECK-NEXT: tail call void @throwAnExceptionOrWhatever() #[[ATTR2]]
; CHECK-NEXT: tail call void @throwAnExceptionOrWhatever() #[[ATTR3]]
; CHECK-NEXT: unreachable
; CHECK: if.end:
; CHECK-NEXT: [[SADD_RESULT:%.*]] = extractvalue { i8, i1 } [[SADD]], 0
Expand Down Expand Up @@ -150,7 +150,7 @@ define i32 @test8(i64 %a, i64 %b) nounwind ssp {
; CHECK-NEXT: [[TMP1:%.*]] = icmp ult i64 [[TMP0]], -4294967296
; CHECK-NEXT: br i1 [[TMP1]], label [[IF_THEN:%.*]], label [[IF_END:%.*]]
; CHECK: if.then:
; CHECK-NEXT: tail call void @throwAnExceptionOrWhatever() #[[ATTR2]]
; CHECK-NEXT: tail call void @throwAnExceptionOrWhatever() #[[ATTR3]]
; CHECK-NEXT: br label [[IF_END]]
; CHECK: if.end:
; CHECK-NEXT: [[CONV9:%.*]] = trunc i64 [[ADD]] to i32
Expand All @@ -171,3 +171,91 @@ if.end:
ret i32 %conv9
}

define i32 @uadd_no_overflow(i32 %a, i32 %b) {
; CHECK-LABEL: @uadd_no_overflow(
; CHECK-NEXT: [[TMP1:%.*]] = add nuw i32 [[A:%.*]], [[B:%.*]]
; CHECK-NEXT: ret i32 [[TMP1]]
;
%val = tail call { i32, i1 } @llvm.uadd.with.overflow.i32(i32 %a, i32 %b)
%ov = extractvalue { i32, i1 } %val, 1
%nowrap = xor i1 %ov, true
tail call void @llvm.assume(i1 %nowrap)
%res = extractvalue { i32, i1 } %val, 0
ret i32 %res
}

define i32 @smul_no_overflow(i32 %a, i32 %b) {
; CHECK-LABEL: @smul_no_overflow(
; CHECK-NEXT: [[TMP1:%.*]] = mul nsw i32 [[A:%.*]], [[B:%.*]]
; CHECK-NEXT: ret i32 [[TMP1]]
;
%val = tail call { i32, i1 } @llvm.smul.with.overflow.i32(i32 %a, i32 %b)
%ov = extractvalue { i32, i1 } %val, 1
%nowrap = xor i1 %ov, true
tail call void @llvm.assume(i1 %nowrap)
%res = extractvalue { i32, i1 } %val, 0
ret i32 %res
}

define i32 @smul_overflow(i32 %a, i32 %b) {
; CHECK-LABEL: @smul_overflow(
; CHECK-NEXT: [[VAL:%.*]] = tail call { i32, i1 } @llvm.smul.with.overflow.i32(i32 [[A:%.*]], i32 [[B:%.*]])
; CHECK-NEXT: [[OV:%.*]] = extractvalue { i32, i1 } [[VAL]], 1
; CHECK-NEXT: tail call void @llvm.assume(i1 [[OV]])
; CHECK-NEXT: [[RES:%.*]] = extractvalue { i32, i1 } [[VAL]], 0
; CHECK-NEXT: ret i32 [[RES]]
;
%val = tail call { i32, i1 } @llvm.smul.with.overflow.i32(i32 %a, i32 %b)
%ov = extractvalue { i32, i1 } %val, 1
tail call void @llvm.assume(i1 %ov)
%res = extractvalue { i32, i1 } %val, 0
ret i32 %res
}

define i32 @uadd_no_overflow_invalid1(i32 %a, i32 %b, i1 %cond) {
; CHECK-LABEL: @uadd_no_overflow_invalid1(
; CHECK-NEXT: [[VAL:%.*]] = tail call { i32, i1 } @llvm.uadd.with.overflow.i32(i32 [[A:%.*]], i32 [[B:%.*]])
; CHECK-NEXT: [[RES:%.*]] = extractvalue { i32, i1 } [[VAL]], 0
; CHECK-NEXT: call void @use(i32 [[RES]])
; CHECK-NEXT: br i1 [[COND:%.*]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
; CHECK: if.then:
; CHECK-NEXT: [[OV:%.*]] = extractvalue { i32, i1 } [[VAL]], 1
; CHECK-NEXT: [[NOWRAP:%.*]] = xor i1 [[OV]], true
; CHECK-NEXT: tail call void @llvm.assume(i1 [[NOWRAP]])
; CHECK-NEXT: ret i32 [[RES]]
; CHECK: if.else:
; CHECK-NEXT: ret i32 0
;
%val = tail call { i32, i1 } @llvm.uadd.with.overflow.i32(i32 %a, i32 %b)
%res = extractvalue { i32, i1 } %val, 0
call void @use(i32 %res)
br i1 %cond, label %if.then, label %if.else
if.then:
%ov = extractvalue { i32, i1 } %val, 1
%nowrap = xor i1 %ov, true
tail call void @llvm.assume(i1 %nowrap)
ret i32 %res
if.else:
ret i32 0
}

define i32 @uadd_no_overflow_invalid2(i32 %a, i32 %b, i1 %cond) {
; CHECK-LABEL: @uadd_no_overflow_invalid2(
; CHECK-NEXT: [[VAL:%.*]] = tail call { i32, i1 } @llvm.uadd.with.overflow.i32(i32 [[A:%.*]], i32 [[B:%.*]])
; CHECK-NEXT: [[OV:%.*]] = extractvalue { i32, i1 } [[VAL]], 1
; CHECK-NEXT: [[NOWRAP:%.*]] = xor i1 [[OV]], true
; CHECK-NEXT: call void @use(i32 0)
; CHECK-NEXT: tail call void @llvm.assume(i1 [[NOWRAP]])
; CHECK-NEXT: [[RES:%.*]] = extractvalue { i32, i1 } [[VAL]], 0
; CHECK-NEXT: ret i32 [[RES]]
;
%val = tail call { i32, i1 } @llvm.uadd.with.overflow.i32(i32 %a, i32 %b)
%ov = extractvalue { i32, i1 } %val, 1
%nowrap = xor i1 %ov, true
call void @use(i32 0) ; It is not guaranteed to transfer execution to its successors
tail call void @llvm.assume(i1 %nowrap)
%res = extractvalue { i32, i1 } %val, 0
ret i32 %res
}

declare void @use(i32)

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