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[InstCombine] Don't miscompile safe increment idiom

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We cleverly handle cases where computation done in one argument of a select
instruction is suitable for the other operand, thus obviating the need
of the select and the comparison.  However, the other operand cannot
have flags.

This fixes PR23757.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@239115 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Majnemer 2015-06-04 23:11:30 +00:00
parent bb3883dfba
commit b0b8cde9d4
2 changed files with 31 additions and 3 deletions
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24
lib/Transforms/InstCombine/InstCombineSelect.cpp
View File

@ -292,10 +292,28 @@ static Value *SimplifyWithOpReplaced(Value *V, Value *Op, Value *RepOp,
// If this is a binary operator, try to simplify it with the replaced op.
if (BinaryOperator *B = dyn_cast<BinaryOperator>(I)) {
Value *Simplified = nullptr;
if (B->getOperand(0) == Op)
return SimplifyBinOp(B->getOpcode(), RepOp, B->getOperand(1), DL, TLI);
if (B->getOperand(1) == Op)
return SimplifyBinOp(B->getOpcode(), B->getOperand(0), RepOp, DL, TLI);
Simplified =
SimplifyBinOp(B->getOpcode(), RepOp, B->getOperand(1), DL, TLI);
if (!Simplified && B->getOperand(1) == Op)
Simplified =
SimplifyBinOp(B->getOpcode(), B->getOperand(0), RepOp, DL, TLI);
if (Simplified) {
// Consider:
// %cmp = icmp eq i32 %x, 2147483647
// %add = add nsw i32 %x, 1
// %sel = select i1 %cmp, i32 -2147483648, i32 %add
//
// We can't replace %sel with %add unless we strip away the flags.
if (isa<OverflowingBinaryOperator>(B)) {
B->setHasNoSignedWrap(false);
B->setHasNoUnsignedWrap(false);
}
if (isa<PossiblyExactOperator>(B))
B->setIsExact(false);
}
return Simplified;
}
// Same for CmpInsts.

10
test/Transforms/InstCombine/select.ll
View File

@ -1532,3 +1532,13 @@ define i32 @test_max_of_min(i32 %a) {
%s1 = select i1 %c1, i32 %s0, i32 -1
ret i32 %s1
}
define i32 @PR23757(i32 %x) {
; CHECK-LABEL: @PR23757
; CHECK: %[[add:.*]] = add i32 %x, 1
; CHECK-NEXT: ret i32 %[[add]]
%cmp = icmp eq i32 %x, 2147483647
%add = add nsw i32 %x, 1
%sel = select i1 %cmp, i32 -2147483648, i32 %add
ret i32 %sel
}