[llvm] ff17da3 - [InstCombine] Push negation through multiply (PR44234)

[Nikita Popov via llvm-commits]

Author: Nikita Popov
Date: 2020-01-31T20:58:55+01:00
New Revision: ff17da3f75b4825f71e81e1caa2e5084d500a1a1

URL: https://github.com/llvm/llvm-project/commit/ff17da3f75b4825f71e81e1caa2e5084d500a1a1
DIFF: https://github.com/llvm/llvm-project/commit/ff17da3f75b4825f71e81e1caa2e5084d500a1a1.diff

LOG: [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

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
    llvm/test/Transforms/InstCombine/mul.ll
    llvm/test/Transforms/InstCombine/sub.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index e15c3d703775..bded1d7cb7ce 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -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;
   }

diff  --git a/llvm/test/Transforms/InstCombine/mul.ll b/llvm/test/Transforms/InstCombine/mul.ll
index be8b2459ef8f..3fc1cc54ea3a 100644
--- a/llvm/test/Transforms/InstCombine/mul.ll
+++ b/llvm/test/Transforms/InstCombine/mul.ll
@@ -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

diff  --git a/llvm/test/Transforms/InstCombine/sub.ll b/llvm/test/Transforms/InstCombine/sub.ll
index 29fb68292848..b291fb89a984 100644
--- a/llvm/test/Transforms/InstCombine/sub.ll
+++ b/llvm/test/Transforms/InstCombine/sub.ll
@@ -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