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Instcombine was illegally transforming -X/C into X/-C when either X or C

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overflowed on negation. This commit checks to make sure that neithe C nor X
overflows. This requires that the RHS of X (a subtract instruction) be a
constant integer.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@60275 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Bill Wendling 2008-11-30 03:42:12 +00:00
parent 4a69bade23
commit e1196d6d3e
4 changed files with 52 additions and 9 deletions
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23
lib/Transforms/Scalar/InstructionCombining.cpp
View File

@ -2956,9 +2956,26 @@ Instruction *InstCombiner::visitSDiv(BinaryOperator &I) {
if (RHS->isAllOnesValue())
return BinaryOperator::CreateNeg(Op0);
// -X/C -> X/-C
if (Value *LHSNeg = dyn_castNegVal(Op0))
return BinaryOperator::CreateSDiv(LHSNeg, ConstantExpr::getNeg(RHS));
ConstantInt *RHSNeg = cast<ConstantInt>(ConstantExpr::getNeg(RHS));
// -X/C -> X/-C, if and only if negation doesn't overflow.
if ((RHS->getSExtValue() < 0 &&
RHS->getSExtValue() < RHSNeg->getSExtValue()) ||
(RHS->getSExtValue() > 0 &&
RHS->getSExtValue() > RHSNeg->getSExtValue())) {
if (Value *LHSNeg = dyn_castNegVal(Op0)) {
if (ConstantInt *CI = dyn_cast<ConstantInt>(LHSNeg)) {
ConstantInt *CINeg = cast<ConstantInt>(ConstantExpr::getNeg(CI));
if ((CI->getSExtValue() < 0 &&
CI->getSExtValue() < CINeg->getSExtValue()) ||
(CI->getSExtValue() > 0 &&
CI->getSExtValue() > CINeg->getSExtValue()))
return BinaryOperator::CreateSDiv(LHSNeg,
ConstantExpr::getNeg(RHS));
}
}
}
}
// If the sign bits of both operands are zero (i.e. we can prove they are

8
test/Transforms/InstCombine/apint-sub.ll
View File

@ -3,7 +3,7 @@
;
; RUN: llvm-as < %s | opt -instcombine | llvm-dis | \
; RUN: grep -v {sub i19 %Cok, %Bok} | not grep sub
; RUN: grep -v {sub i19 %Cok, %Bok} | grep -v {sub i25 0, %Aok} | not grep sub
; END.
define i23 @test1(i23 %A) {
@ -107,8 +107,10 @@ define i51 @test16(i51 %A) {
ret i51 %Y
}
define i25 @test17(i25 %A) {
%B = sub i25 0, %A ; <i25> [#uses=1]
; Can't fold subtract here because negation it might oveflow.
; PR3142
define i25 @test17(i25 %Aok) {
%B = sub i25 0, %Aok ; <i25> [#uses=1]
%C = sdiv i25 %B, 1234 ; <i25> [#uses=1]
ret i25 %C
}

22
test/Transforms/InstCombine/sdiv-1.ll Normal file
View File

@ -0,0 +1,22 @@
; RUN: llvm-as < %s | opt -instcombine -inline | llvm-dis | grep {715827882} | count 2
; PR3142
define i32 @a(i32 %X) nounwind readnone {
entry:
%0 = sub i32 0, %X
%1 = sdiv i32 %0, -3
ret i32 %1
}
define i32 @b(i32 %X) nounwind readnone {
entry:
%0 = call i32 @a(i32 -2147483648)
ret i32 %0
}
define i32 @c(i32 %X) nounwind readnone {
entry:
%0 = sub i32 0, -2147483648
%1 = sdiv i32 %0, -3
ret i32 %1
}

8
test/Transforms/InstCombine/sub.ll
View File

@ -1,7 +1,7 @@
; This test makes sure that these instructions are properly eliminated.
;
; RUN: llvm-as < %s | opt -instcombine | llvm-dis | \
; RUN: grep -v {sub i32 %Cok, %Bok} | not grep sub
; RUN: grep -v {sub i32 %Cok, %Bok} | grep -v {sub i32 0, %Aok} | not grep sub
define i32 @test1(i32 %A) {
%B = sub i32 %A, %A ; <i32> [#uses=1]
@ -104,8 +104,10 @@ define i32 @test16(i32 %A) {
ret i32 %Y
}
define i32 @test17(i32 %A) {
%B = sub i32 0, %A ; <i32> [#uses=1]
; Can't fold subtract here because negation it might oveflow.
; PR3142
define i32 @test17(i32 %Aok) {
%B = sub i32 0, %Aok ; <i32> [#uses=1]
%C = sdiv i32 %B, 1234 ; <i32> [#uses=1]
ret i32 %C
}