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Give the Reassociate pass a bit more flexibility and autonomy when optimizing expressions.

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Particularly, it addresses cases where Reassociate breaks Subtracts but then fails to optimize combinations like I1 + -I2 where I1 and I2 have the same rank and are identical.

Patch by Dmitri Shtilman.

llvm-svn: 219092
This commit is contained in:
Owen Anderson 2014-10-05 23:41:26 +00:00
parent 88628181c0
commit 2aa1295ade
2 changed files with 27 additions and 2 deletions
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14
lib/Transforms/Scalar/Reassociate.cpp
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@ -1034,13 +1034,23 @@ static unsigned FindInOperandList(SmallVectorImpl<ValueEntry> &Ops, unsigned i,
Value *X) {
unsigned XRank = Ops[i].Rank;
unsigned e = Ops.size();
for (unsigned j = i+1; j != e && Ops[j].Rank == XRank; ++j)
for (unsigned j = i+1; j != e && Ops[j].Rank == XRank; ++j) {
if (Ops[j].Op == X)
return j;
if (Instruction *I1 = dyn_cast<Instruction>(Ops[j].Op))
if (Instruction *I2 = dyn_cast<Instruction>(X))
if (I1->isIdenticalTo(I2))
return j;
}
// Scan backwards.
for (unsigned j = i-1; j != ~0U && Ops[j].Rank == XRank; --j)
for (unsigned j = i-1; j != ~0U && Ops[j].Rank == XRank; --j) {
if (Ops[j].Op == X)
return j;
if (Instruction *I1 = dyn_cast<Instruction>(Ops[j].Op))
if (Instruction *I2 = dyn_cast<Instruction>(X))
if (I1->isIdenticalTo(I2))
return j;
}
return i;
}

15
test/Transforms/Reassociate/negation1.ll Normal file
View File

@ -0,0 +1,15 @@
; RUN: opt < %s -reassociate -instcombine -S | FileCheck %s
; Test that we can turn things like A*B + X - A*B -> X.
define i32 @test1(i32 %a, i32 %b, i32 %x) {
; CHECK-LABEL: test1
; CHECK: ret i32 %x
%c = mul i32 %a, %b
%d = add i32 %c, %x
%c1 = mul i32 %a, %b
%f = sub i32 %d, %c1
ret i32 %f
}