[llvm] 3e6ba89 - [InstCombine] Fold a mul with bool value into and

[via llvm-commits]

Author: zhongyunde
Date: 2022-05-30T21:05:00+08:00
New Revision: 3e6ba89055c80e6360b7605464520711b30084a6

URL: https://github.com/llvm/llvm-project/commit/3e6ba89055c80e6360b7605464520711b30084a6
DIFF: https://github.com/llvm/llvm-project/commit/3e6ba89055c80e6360b7605464520711b30084a6.diff

LOG: [InstCombine] Fold a mul with bool value into and

Fixes https://github.com/llvm/llvm-project/issues/55599
  X * Y --> X & Y, iff X, Y can be only {0, 1}.
https://alive2.llvm.org/ce/z/_RsTKF

Reviewed By: spatel, nikic

Differential Revision: https://reviews.llvm.org/D126040

Added: 
    

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

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
index 897580a414876..da31d6260c88b 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
@@ -301,9 +301,15 @@ Instruction *InstCombinerImpl::visitMul(BinaryOperator &I) {
     }
   }
 
-  // i1 mul -> i1 and.
+  // Fold the following two scenarios:
+  //   1) i1 mul -> i1 and.
+  //   2) X * Y --> X & Y, iff X, Y can be only {0,1}.
+  // Note: We could use known bits to generalize this and related patterns with
+  // shifts/truncs
   Type *Ty = I.getType();
-  if (Ty->isIntOrIntVectorTy(1))
+  if (Ty->isIntOrIntVectorTy(1) ||
+      (match(Op0, m_And(m_Value(), m_One())) &&
+       match(Op1, m_And(m_Value(), m_One()))))
     return BinaryOperator::CreateAnd(Op0, Op1);
 
   // X*(1 << Y) --> X << Y

diff  --git a/llvm/test/Transforms/InstCombine/mul-masked-bits.ll b/llvm/test/Transforms/InstCombine/mul-masked-bits.ll
index 553788561f759..9b7caff982865 100644
--- a/llvm/test/Transforms/InstCombine/mul-masked-bits.ll
+++ b/llvm/test/Transforms/InstCombine/mul-masked-bits.ll
@@ -169,13 +169,31 @@ define i33 @squared_demanded_3_low_bits(i33 %x) {
 ; Scalar tests
 define i64 @scalar_mul_bit_x0_y0(i64 %x, i64 %y) {
 ; CHECK-LABEL: @scalar_mul_bit_x0_y0(
+; CHECK-NEXT:    [[AND2:%.*]] = and i64 [[Y:%.*]], 1
+; CHECK-NEXT:    [[MUL:%.*]] = and i64 [[AND2]], [[X:%.*]]
+; CHECK-NEXT:    ret i64 [[MUL]]
+;
+  %and1 = and i64 %x, 1
+  %and2 = and i64 %y, 1
+  %mul = mul i64 %and1, %and2
+  ret i64 %mul
+}
+
+declare void @use(i64)
+
+define i64 @scalar_mul_bit_x0_y0_uses(i64 %x, i64 %y) {
+; CHECK-LABEL: @scalar_mul_bit_x0_y0_uses(
 ; CHECK-NEXT:    [[AND1:%.*]] = and i64 [[X:%.*]], 1
+; CHECK-NEXT:    call void @use(i64 [[AND1]])
 ; CHECK-NEXT:    [[AND2:%.*]] = and i64 [[Y:%.*]], 1
-; CHECK-NEXT:    [[MUL:%.*]] = mul nuw nsw i64 [[AND1]], [[AND2]]
+; CHECK-NEXT:    call void @use(i64 [[AND2]])
+; CHECK-NEXT:    [[MUL:%.*]] = and i64 [[AND2]], [[X]]
 ; CHECK-NEXT:    ret i64 [[MUL]]
 ;
   %and1 = and i64 %x, 1
+  call void @use(i64 %and1)
   %and2 = and i64 %y, 1
+  call void @use(i64 %and2)
   %mul = mul i64 %and1, %and2
   ret i64 %mul
 }
@@ -210,9 +228,8 @@ define i64 @scalar_mul_bit_x0_yC(i64 %x, i64 %y, i64 %c) {
 ; Vector tests
 define <2 x i64> @vector_mul_bit_x0_y0(<2 x i64> %x, <2 x i64> %y) {
 ; CHECK-LABEL: @vector_mul_bit_x0_y0(
-; CHECK-NEXT:    [[AND1:%.*]] = and <2 x i64> [[X:%.*]], <i64 1, i64 1>
 ; CHECK-NEXT:    [[AND2:%.*]] = and <2 x i64> [[Y:%.*]], <i64 1, i64 1>
-; CHECK-NEXT:    [[MUL:%.*]] = mul nuw nsw <2 x i64> [[AND1]], [[AND2]]
+; CHECK-NEXT:    [[MUL:%.*]] = and <2 x i64> [[AND2]], [[X:%.*]]
 ; CHECK-NEXT:    ret <2 x i64> [[MUL]]
 ;
   %and1 = and <2 x i64> %x, <i64 1, i64 1>