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[InstCombine] sub X, sext(bool Y) -> add X, zext(bool Y)

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Prefer add/zext because they are better supported in terms of value-tracking.

Note that the backend should be prepared for this IR canonicalization 
(including vector types) after:
https://reviews.llvm.org/rL284015

Differential Revision: https://reviews.llvm.org/D25135

llvm-svn: 284241
This commit is contained in:
Sanjay Patel 2016-10-14 15:24:31 +00:00
parent 96ecdb67e0
commit 8024bbbb08
3 changed files with 66 additions and 3 deletions
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11
lib/Transforms/InstCombine/InstCombineAddSub.cpp
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@ -1642,6 +1642,17 @@ Instruction *InstCombiner::visitSub(BinaryOperator &I) {
if (Value *XNeg = dyn_castNegVal(X))
return BinaryOperator::CreateShl(XNeg, Y);
// Subtracting -1/0 is the same as adding 1/0:
// sub [nsw] Op0, sext(bool Y) -> add [nsw] Op0, zext(bool Y)
// 'nuw' is dropped in favor of the canonical form.
if (match(Op1, m_SExt(m_Value(Y))) &&
Y->getType()->getScalarSizeInBits() == 1) {
Value *Zext = Builder->CreateZExt(Y, I.getType());
BinaryOperator *Add = BinaryOperator::CreateAdd(Op0, Zext);
Add->setHasNoSignedWrap(I.hasNoSignedWrap());
return Add;
}
// X - A*-B -> X + A*B
// X - -A*B -> X + A*B
Value *A, *B;

53
test/Transforms/InstCombine/sub.ll
View File

@ -639,3 +639,56 @@ define i32 @test48(i1 %A, i32 %B, i32 %C, i32 %D) {
%sub = sub i32 %sel0, %sel1
ret i32 %sub
}
; Zext+add is more canonical than sext+sub.
define i8 @bool_sext_sub(i8 %x, i1 %y) {
; CHECK-LABEL: @bool_sext_sub(
; CHECK-NEXT: [[TMP1:%.*]] = zext i1 %y to i8
; CHECK-NEXT: [[SUB:%.*]] = add i8 [[TMP1]], %x
; CHECK-NEXT: ret i8 [[SUB]]
;
%sext = sext i1 %y to i8
%sub = sub i8 %x, %sext
ret i8 %sub
}
; Vectors get the same transform.
define <2 x i8> @bool_sext_sub_vec(<2 x i8> %x, <2 x i1> %y) {
; CHECK-LABEL: @bool_sext_sub_vec(
; CHECK-NEXT: [[TMP1:%.*]] = zext <2 x i1> %y to <2 x i8>
; CHECK-NEXT: [[SUB:%.*]] = add <2 x i8> [[TMP1]], %x
; CHECK-NEXT: ret <2 x i8> [[SUB]]
;
%sext = sext <2 x i1> %y to <2 x i8>
%sub = sub <2 x i8> %x, %sext
ret <2 x i8> %sub
}
; NSW is preserved.
define <2 x i8> @bool_sext_sub_vec_nsw(<2 x i8> %x, <2 x i1> %y) {
; CHECK-LABEL: @bool_sext_sub_vec_nsw(
; CHECK-NEXT: [[TMP1:%.*]] = zext <2 x i1> %y to <2 x i8>
; CHECK-NEXT: [[SUB:%.*]] = add nsw <2 x i8> [[TMP1]], %x
; CHECK-NEXT: ret <2 x i8> [[SUB]]
;
%sext = sext <2 x i1> %y to <2 x i8>
%sub = sub nsw <2 x i8> %x, %sext
ret <2 x i8> %sub
}
; We favor the canonical zext+add over keeping the NUW.
define i8 @bool_sext_sub_nuw(i8 %x, i1 %y) {
; CHECK-LABEL: @bool_sext_sub_nuw(
; CHECK-NEXT: [[TMP1:%.*]] = zext i1 %y to i8
; CHECK-NEXT: [[SUB:%.*]] = add i8 [[TMP1]], %x
; CHECK-NEXT: ret i8 [[SUB]]
;
%sext = sext i1 %y to i8
%sub = sub nuw i8 %x, %sext
ret i8 %sub
}

5
test/Transforms/InstCombine/urem.ll
View File

@ -25,12 +25,11 @@ define i8 @big_divisor(i8 %x) {
ret i8 %rem
}
; TODO: Should this be zext+add instead of sext+sub?
define i5 @biggest_divisor(i5 %x) {
; CHECK-LABEL: @biggest_divisor(
; CHECK-NEXT: [[NOT_:%.*]] = icmp eq i5 %x, -1
; CHECK-NEXT: [[TMP1:%.*]] = sext i1 [[NOT_]] to i5
; CHECK-NEXT: [[REM:%.*]] = sub i5 %x, [[TMP1]]
; CHECK-NEXT: [[TMP1:%.*]] = zext i1 [[NOT_]] to i5
; CHECK-NEXT: [[REM:%.*]] = add i5 [[TMP1]], %x
; CHECK-NEXT: ret i5 [[REM]]
;
%rem = urem i5 %x, -1