[PATCH] D114729: [InstCombine] try to fold 'or' into 'mul' operand

[Sanjay Patel via Phabricator via llvm-commits]

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or (mul X, C), X --> mul X, C+1  (when the multiply has no common bits with X)

We already have this fold if the pattern ends in 'add', but we can miss it if the 'add' becomes 'or' via another no-common-bits transform:

This is part of fixing:
http://llvm.org/PR49055
...but it won't make a difference on that example yet.

https://alive2.llvm.org/ce/z/Vrmoeb


https://reviews.llvm.org/D114729

Files:
  llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
  llvm/test/Transforms/InstCombine/or.ll


Index: llvm/test/Transforms/InstCombine/or.ll
===================================================================
--- llvm/test/Transforms/InstCombine/or.ll
+++ llvm/test/Transforms/InstCombine/or.ll
@@ -1445,8 +1445,7 @@
 define i32 @mul_no_common_bits(i32 %p) {
 ; CHECK-LABEL: @mul_no_common_bits(
 ; CHECK-NEXT:    [[X:%.*]] = and i32 [[P:%.*]], 7
-; CHECK-NEXT:    [[M:%.*]] = mul nuw nsw i32 [[X]], 24
-; CHECK-NEXT:    [[R:%.*]] = or i32 [[M]], [[X]]
+; CHECK-NEXT:    [[R:%.*]] = mul nuw nsw i32 [[X]], 25
 ; CHECK-NEXT:    ret i32 [[R]]
 ;
   %x = and i32 %p, 7
@@ -1458,8 +1457,7 @@
 define <2 x i12> @mul_no_common_bits_commute(<2 x i12> %p) {
 ; CHECK-LABEL: @mul_no_common_bits_commute(
 ; CHECK-NEXT:    [[X:%.*]] = and <2 x i12> [[P:%.*]], <i12 1, i12 1>
-; CHECK-NEXT:    [[M:%.*]] = mul nuw nsw <2 x i12> [[X]], <i12 14, i12 14>
-; CHECK-NEXT:    [[R:%.*]] = or <2 x i12> [[X]], [[M]]
+; CHECK-NEXT:    [[R:%.*]] = mul nuw nsw <2 x i12> [[X]], <i12 15, i12 15>
 ; CHECK-NEXT:    ret <2 x i12> [[R]]
 ;
   %x = and <2 x i12> %p, <i12 1, i12 1>
@@ -1468,6 +1466,8 @@
   ret <2 x i12> %r
 }
 
+; negative test - probably not good to create an extra mul
+
 define i32 @mul_no_common_bits_uses(i32 %p) {
 ; CHECK-LABEL: @mul_no_common_bits_uses(
 ; CHECK-NEXT:    [[X:%.*]] = and i32 [[P:%.*]], 7
@@ -1482,3 +1482,18 @@
   %r = or i32 %m, %x
   ret i32 %r
 }
+
+; negative test - %x and %m may have set 3rd bit
+
+define i32 @mul_common_bits(i32 %p) {
+; CHECK-LABEL: @mul_common_bits(
+; CHECK-NEXT:    [[X:%.*]] = and i32 [[P:%.*]], 7
+; CHECK-NEXT:    [[M:%.*]] = mul nuw nsw i32 [[X]], 12
+; CHECK-NEXT:    [[R:%.*]] = or i32 [[M]], [[X]]
+; CHECK-NEXT:    ret i32 [[R]]
+;
+  %x = and i32 %p, 7
+  %m = mul i32 %x, 12
+  %r = or i32 %m, %x
+  ret i32 %r
+}
Index: llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -2622,6 +2622,12 @@
     return BinaryOperator::CreateXor(Or, ConstantInt::get(Ty, *CV));
   }
 
+  // or (mul X, CV), X --> mul X, CV+1
+  if (match(&I,
+            m_c_Or(m_OneUse(m_Mul(m_Value(X), m_APInt(CV))), m_Deferred(X))))
+    if (haveNoCommonBitsSet(Op0, Op1, DL))
+      return BinaryOperator::CreateMul(X, ConstantInt::get(Ty, *CV + 1));
+
   // (A & C) | (B & D)
   Value *A, *B, *C, *D;
   if (match(Op0, m_And(m_Value(A), m_Value(C))) &&


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