[PATCH] D73410: [InstCombine] Push negation through multiply (PR44234)

[Nikita Popov via Phabricator via llvm-commits]

nikic updated this revision to Diff 241550.
nikic added a comment.

Rebase over D73411 <https://reviews.llvm.org/D73411>.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D73410/new/

https://reviews.llvm.org/D73410

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


Index: llvm/test/Transforms/InstCombine/sub.ll
===================================================================
--- llvm/test/Transforms/InstCombine/sub.ll
+++ llvm/test/Transforms/InstCombine/sub.ll
@@ -689,10 +689,9 @@
 
 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 @@
   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
Index: llvm/test/Transforms/InstCombine/mul.ll
===================================================================
--- llvm/test/Transforms/InstCombine/mul.ll
+++ llvm/test/Transforms/InstCombine/mul.ll
@@ -456,10 +456,9 @@
 
 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
Index: llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -935,6 +935,15 @@
       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;
   }


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D73410.241550.patch
Type: text/x-patch
Size: 3032 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20200130/6dee9397/attachment.bin>