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Transform (X/Y)*Y into X if the division is exact. Instcombine already knows how

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to do this and more, but would only do it if X/Y had only one use.  Spotted as the
most common missed simplification in SPEC by my auto-simplifier, now that it knows
about nuw/nsw/exact flags.  This removes a bunch of multiplications from 447.dealII
and 483.xalancbmk.  It also removes a lot from tramp3d-v4, which results in much
more inlining.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@124560 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Duncan Sands 2011-01-30 18:03:50 +00:00
parent 9b108a338d
commit 1895e98ef3
2 changed files with 27 additions and 0 deletions
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9
lib/Analysis/InstructionSimplify.cpp
View File

@ -710,6 +710,15 @@ static Value *SimplifyMulInst(Value *Op0, Value *Op1, const TargetData *TD,
if (match(Op1, m_One()))
return Op0;
// (X / Y) * Y -> X if the division is exact.
Value *X = 0, *Y = 0;
if ((match(Op0, m_SDiv(m_Value(X), m_Value(Y))) && Y == Op1) || // (X / Y) * Y
(match(Op1, m_SDiv(m_Value(X), m_Value(Y))) && Y == Op0)) { // Y * (X / Y)
BinaryOperator *SDiv = cast<BinaryOperator>(Y == Op1 ? Op0 : Op1);
if (SDiv->isExact())
return X;
}
// i1 mul -> and.
if (MaxRecurse && Op0->getType()->isIntegerTy(1))
if (Value *V = SimplifyAndInst(Op0, Op1, TD, DT, MaxRecurse-1))

18
test/Transforms/InstSimplify/2010-12-20-Reassociate.ll
View File

@ -119,6 +119,24 @@ define i32 @sdiv3(i32 %x, i32 %y) {
; CHECK: ret i32 0
}
define i32 @sdiv4(i32 %x, i32 %y) {
; CHECK: @sdiv4
; (X / Y) * Y -> X if the division is exact
%div = sdiv exact i32 %x, %y
%mul = mul i32 %div, %y
ret i32 %mul
; CHECK: ret i32 %x
}
define i32 @sdiv5(i32 %x, i32 %y) {
; CHECK: @sdiv5
; Y * (X / Y) -> X if the division is exact
%div = sdiv exact i32 %x, %y
%mul = mul i32 %y, %div
ret i32 %mul
; CHECK: ret i32 %x
}
define i32 @udiv1(i32 %x, i32 %y) {
; CHECK: @udiv1
; (no overflow X * Y) / Y -> X