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Reenable the transform "(X*Y)/Y->X" when the multiplication is known not to

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overflow (nsw flag), which was disabled because it breaks 254.gap.  I have
informed the GAP authors of the mistake in their code, and arranged for the
testsuite to use -fwrapv when compiling this benchmark.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@124746 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Duncan Sands 2011-02-02 20:52:00 +00:00
parent 79fcb6dec3
commit 4b720718fb
2 changed files with 9 additions and 5 deletions
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10
lib/Analysis/InstructionSimplify.cpp
View File

@ -798,11 +798,11 @@ static Value *SimplifyDiv(unsigned Opcode, Value *Op0, Value *Op1,
Value *X = 0, *Y = 0;
if (match(Op0, m_Mul(m_Value(X), m_Value(Y))) && (X == Op1 || Y == Op1)) {
if (Y != Op1) std::swap(X, Y); // Ensure expression is (X * Y) / Y, Y = Op1
// BinaryOperator *Mul = cast<BinaryOperator>(Op0);
// // If the Mul knows it does not overflow, then we are good to go.
// if ((isSigned && Mul->hasNoSignedWrap()) ||
// (!isSigned && Mul->hasNoUnsignedWrap()))
// return X;
BinaryOperator *Mul = cast<BinaryOperator>(Op0);
// If the Mul knows it does not overflow, then we are good to go.
if ((isSigned && Mul->hasNoSignedWrap()) ||
(!isSigned && Mul->hasNoUnsignedWrap()))
return X;
// If X has the form X = A / Y then X * Y cannot overflow.
if (BinaryOperator *Div = dyn_cast<BinaryOperator>(X))
if (Div->getOpcode() == Opcode && Div->getOperand(1) == Y)

4
test/Transforms/InstSimplify/2010-12-20-Reassociate.ll
View File

@ -92,10 +92,12 @@ define i32 @sub3(i32 %x, i32 %y) {
}
define i32 @sdiv1(i32 %x, i32 %y) {
; CHECK: @sdiv1
; (no overflow X * Y) / Y -> X
%mul = mul nsw i32 %x, %y
%r = sdiv i32 %mul, %y
ret i32 %r
; CHECK: ret i32 %x
}
define i32 @sdiv2(i32 %x, i32 %y) {
@ -136,10 +138,12 @@ define i32 @sdiv5(i32 %x, i32 %y) {
}
define i32 @udiv1(i32 %x, i32 %y) {
; CHECK: @udiv1
; (no overflow X * Y) / Y -> X
%mul = mul nuw i32 %x, %y
%r = udiv i32 %mul, %y
ret i32 %r
; CHECK: ret i32 %x
}
define i32 @udiv2(i32 %x, i32 %y) {