[llvm] a7a2860 - [InstCombine] convert mul with sexted bool and constant to select

[Sanjay Patel via llvm-commits]

Author: Sanjay Patel
Date: 2022-01-20T15:57:01-05:00
New Revision: a7a2860d0eee37d9e0fd0b6a8e3d884f8ee4ec16

URL: https://github.com/llvm/llvm-project/commit/a7a2860d0eee37d9e0fd0b6a8e3d884f8ee4ec16
DIFF: https://github.com/llvm/llvm-project/commit/a7a2860d0eee37d9e0fd0b6a8e3d884f8ee4ec16.diff

LOG: [InstCombine] convert mul with sexted bool and constant to select

We already have the related folds for zext-of-bool, so it
should make things more consistent to have this transform
to select for sext-of-bool too:
https://alive2.llvm.org/ce/z/YikdfA

Fixes #53319

Added: 
    

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

Removed: 
    


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diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index aca7ec8d7325a..076c3134d0782 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -348,13 +348,21 @@ Instruction *InstCombinerImpl::visitMul(BinaryOperator &I) {
     return CastInst::Create(Instruction::SExt, And, I.getType());
   }
 
-  // (bool X) * Y --> X ? Y : 0
-  // Y * (bool X) --> X ? Y : 0
+  // (zext bool X) * Y --> X ? Y : 0
+  // Y * (zext bool X) --> X ? Y : 0
   if (match(Op0, m_ZExt(m_Value(X))) && X->getType()->isIntOrIntVectorTy(1))
     return SelectInst::Create(X, Op1, ConstantInt::get(I.getType(), 0));
   if (match(Op1, m_ZExt(m_Value(X))) && X->getType()->isIntOrIntVectorTy(1))
     return SelectInst::Create(X, Op0, ConstantInt::get(I.getType(), 0));
 
+  // (sext bool X) * C --> X ? -C : 0
+  Constant *ImmC;
+  if (match(Op0, m_SExt(m_Value(X))) && X->getType()->isIntOrIntVectorTy(1) &&
+      match(Op1, m_ImmConstant(ImmC))) {
+    Constant *NegC = ConstantExpr::getNeg(ImmC);
+    return SelectInst::Create(X, NegC, ConstantInt::getNullValue(I.getType()));
+  }
+
   // (lshr X, 31) * Y --> (ashr X, 31) & Y
   // Y * (lshr X, 31) --> (ashr X, 31) & Y
   // TODO: We are not checking one-use because the elimination of the multiply

diff  --git a/llvm/test/Transforms/InstCombine/mul.ll b/llvm/test/Transforms/InstCombine/mul.ll
index e99d1e9cfd181..56947040f78a9 100644
--- a/llvm/test/Transforms/InstCombine/mul.ll
+++ b/llvm/test/Transforms/InstCombine/mul.ll
@@ -133,8 +133,7 @@ define <2 x i32> @mul_bool_vec_commute(<2 x i32> %px, <2 x i1> %y) {
 
 define i32 @mul_sext_bool(i1 %x) {
 ; CHECK-LABEL: @mul_sext_bool(
-; CHECK-NEXT:    [[S:%.*]] = sext i1 [[X:%.*]] to i32
-; CHECK-NEXT:    [[M:%.*]] = mul nsw i32 [[S]], 42
+; CHECK-NEXT:    [[M:%.*]] = select i1 [[X:%.*]], i32 -42, i32 0
 ; CHECK-NEXT:    ret i32 [[M]]
 ;
   %s = sext i1 %x to i32
@@ -146,7 +145,7 @@ define i32 @mul_sext_bool_use(i1 %x) {
 ; CHECK-LABEL: @mul_sext_bool_use(
 ; CHECK-NEXT:    [[S:%.*]] = sext i1 [[X:%.*]] to i32
 ; CHECK-NEXT:    call void @use32(i32 [[S]])
-; CHECK-NEXT:    [[M:%.*]] = mul nsw i32 [[S]], 42
+; CHECK-NEXT:    [[M:%.*]] = select i1 [[X]], i32 -42, i32 0
 ; CHECK-NEXT:    ret i32 [[M]]
 ;
   %s = sext i1 %x to i32
@@ -157,8 +156,7 @@ define i32 @mul_sext_bool_use(i1 %x) {
 
 define <2 x i8> @mul_sext_bool_vec(<2 x i1> %x) {
 ; CHECK-LABEL: @mul_sext_bool_vec(
-; CHECK-NEXT:    [[S:%.*]] = sext <2 x i1> [[X:%.*]] to <2 x i8>
-; CHECK-NEXT:    [[M:%.*]] = mul <2 x i8> [[S]], <i8 42, i8 -128>
+; CHECK-NEXT:    [[M:%.*]] = select <2 x i1> [[X:%.*]], <2 x i8> <i8 -42, i8 -128>, <2 x i8> zeroinitializer
 ; CHECK-NEXT:    ret <2 x i8> [[M]]
 ;
   %s = sext <2 x i1> %x to <2 x i8>