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InstCombine: Implement X - A*-B -> X + A*B.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@119984 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Benjamin Kramer 2010-11-22 20:31:27 +00:00
parent 28ef0a5719
commit 93f8455d73
3 changed files with 29 additions and 16 deletions
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16
lib/Target/README.txt
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@ -1736,22 +1736,6 @@ Another similar case involves truncations on 64-bit targets:
...
%367 = icmp eq i32 %362, 0 ; [#uses=1]
//===---------------------------------------------------------------------===//
Missed instcombine/dagcombine transformation:
define i32 @a(i32 %x, i32 %y) nounwind readnone {
entry:
%mul = mul i32 %y, -8
%sub = sub i32 %x, %mul
ret i32 %sub
}
Should compile to something like x+y*8, but currently compiles to an
inefficient result. Testcase derived from gcc. C testcase:
int a(int x, int y) { return y-x*-8; }
//===---------------------------------------------------------------------===//
Missed instcombine/dagcombine transformation:

9
lib/Transforms/InstCombine/InstCombineAddSub.cpp
View File

@ -675,6 +675,15 @@ Instruction *InstCombiner::visitSub(BinaryOperator &I) {
C2);
return BinaryOperator::CreateMul(Op0, CP1);
}
// X - A*-B -> X + A*B
// X - -A*B -> X + A*B
Value *A, *B;
if (match(Op1I, m_Mul(m_Value(A), m_Neg(m_Value(B)))) ||
match(Op1I, m_Mul(m_Neg(m_Value(A)), m_Value(B)))) {
Value *NewMul = Builder->CreateMul(A, B);
return BinaryOperator::CreateAdd(Op0, NewMul);
}
}
}

20
test/Transforms/InstCombine/sub.ll
View File

@ -281,3 +281,23 @@ define i32 @test26(i32 %x) {
; CHECK-NEXT: ret i32
}
define i32 @test27(i32 %x, i32 %y) {
%mul = mul i32 %y, -8
%sub = sub i32 %x, %mul
ret i32 %sub
; CHECK: @test27
; CHECK-NEXT: shl i32 %y, 3
; CHECK-NEXT: add i32
; CHECK-NEXT: ret i32
}
define i32 @test28(i32 %x, i32 %y, i32 %z) {
%neg = sub i32 0, %z
%mul = mul i32 %neg, %y
%sub = sub i32 %x, %mul
ret i32 %sub
; CHECK: @test28
; CHECK-NEXT: mul i32 %z, %y
; CHECK-NEXT: add i32
; CHECK-NEXT: ret i32
}