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[InstCombine] Push negation through multiply (PR44234) 

Fixes https://bugs.llvm.org/show_bug.cgi?id=44234 by adding
multiply support to freelyNegateValue(). Only one of the operands
needs to be negatible, so this still fits within the framework.

Differential Revision: https://reviews.llvm.org/D73410
This commit is contained in:
Nikita Popov 2020-01-24 22:11:41 +01:00
parent 2a6ef2aecf
commit ff17da3f75
3 changed files with 20 additions and 14 deletions
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9
llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
View File

@ -935,6 +935,15 @@ Value *InstCombiner::freelyNegateValue(Value *V) {
return Builder.CreateTrunc(NegA, I->getType(), I->getName() + ".neg");
return nullptr;
// 0-(A*B) => (0-A)*B
// 0-(A*B) => A*(0-B)
case Instruction::Mul:
if (Value *NegA = freelyNegateValue(I->getOperand(0)))
return Builder.CreateMul(NegA, I->getOperand(1), V->getName() + ".neg");
if (Value *NegB = freelyNegateValue(I->getOperand(1)))
return Builder.CreateMul(I->getOperand(0), NegB, V->getName() + ".neg");
return nullptr;
default:
return nullptr;
}

7
llvm/test/Transforms/InstCombine/mul.ll
View File

@ -456,10 +456,9 @@ define i32 @test_mul_canonicalize_op0(i32 %x, i32 %y) {
define i32 @test_mul_canonicalize_op1(i32 %x, i32 %z) {
; CHECK-LABEL: @test_mul_canonicalize_op1(
; CHECK-NEXT: [[Y:%.*]] = mul i32 [[Z:%.*]], 3
; CHECK-NEXT: [[TMP1:%.*]] = mul i32 [[Y]], [[X:%.*]]
; CHECK-NEXT: [[MUL:%.*]] = sub i32 0, [[TMP1]]
; CHECK-NEXT: ret i32 [[MUL]]
; CHECK-NEXT: [[Y_NEG:%.*]] = mul i32 [[Z:%.*]], -3
; CHECK-NEXT: [[DOTNEG:%.*]] = mul i32 [[Y_NEG]], [[X:%.*]]
; CHECK-NEXT: ret i32 [[DOTNEG]]
;
%y = mul i32 %z, 3
%neg = sub i32 0, %x

18
llvm/test/Transforms/InstCombine/sub.ll
View File

@ -689,10 +689,9 @@ define i32 @test_neg_trunc_shl_lshr(i64 %a, i64 %b) {
define i64 @test_neg_mul_sub(i64 %a, i64 %b, i64 %c) {
; CHECK-LABEL: @test_neg_mul_sub(
; CHECK-NEXT: [[SUB:%.*]] = sub i64 [[A:%.*]], [[B:%.*]]
; CHECK-NEXT: [[MUL:%.*]] = mul i64 [[SUB]], [[C:%.*]]
; CHECK-NEXT: [[NEG:%.*]] = sub i64 0, [[MUL]]
; CHECK-NEXT: ret i64 [[NEG]]
; CHECK-NEXT: [[SUB_NEG:%.*]] = sub i64 [[B:%.*]], [[A:%.*]]
; CHECK-NEXT: [[MUL_NEG:%.*]] = mul i64 [[SUB_NEG]], [[C:%.*]]
; CHECK-NEXT: ret i64 [[MUL_NEG]]
;
%sub = sub i64 %a, %b
%mul = mul i64 %sub, %c
@ -700,13 +699,12 @@ define i64 @test_neg_mul_sub(i64 %a, i64 %b, i64 %c) {
ret i64 %neg
}
define i64 @test_neg_mul_sub_communted(i64 %a, i64 %b, i64 %c) {
; CHECK-LABEL: @test_neg_mul_sub_communted(
define i64 @test_neg_mul_sub_commuted(i64 %a, i64 %b, i64 %c) {
; CHECK-LABEL: @test_neg_mul_sub_commuted(
; CHECK-NEXT: [[COMPLEX:%.*]] = mul i64 [[C:%.*]], [[C]]
; CHECK-NEXT: [[SUB:%.*]] = sub i64 [[A:%.*]], [[B:%.*]]
; CHECK-NEXT: [[MUL:%.*]] = mul i64 [[COMPLEX]], [[SUB]]
; CHECK-NEXT: [[NEG:%.*]] = sub i64 0, [[MUL]]
; CHECK-NEXT: ret i64 [[NEG]]
; CHECK-NEXT: [[SUB_NEG:%.*]] = sub i64 [[B:%.*]], [[A:%.*]]
; CHECK-NEXT: [[MUL_NEG:%.*]] = mul i64 [[COMPLEX]], [[SUB_NEG]]
; CHECK-NEXT: ret i64 [[MUL_NEG]]
;
%complex = mul i64 %c, %c
%sub = sub i64 %a, %b