[InstSimplify] Handle (~A & ~B) | (~A ^ B) -> ~A ^ B

The code Sanjay Patel moved over from InstCombine doesn't work properly if the 'and' has both inputs as nots because we used a commuted op matcher on the 'and' first. But this will bind to the first 'not' on 'and' when there could be two 'not's. InstCombine could rely on DeMorgan to ensure the 'and' wouldn't have two 'not's eventually, but InstSimplify can't rely on that.

This patch matches the xor first then checks for the ands and allows a not of either operand of the xor.

Differential Revision: https://reviews.llvm.org/D32458

llvm-svn: 301329

2 files changed, 72 insertions, 4 deletions

diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index be9beebe189..febaf302ef3 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -1886,15 +1886,21 @@ static Value *SimplifyOrInst(Value *Op0, Value *Op1, const Query &Q,
 
   // (A & ~B) | (A ^ B) -> (A ^ B)
   // (~B & A) | (A ^ B) -> (A ^ B)
-  if (match(Op0, m_c_And(m_Value(A), m_Not(m_Value(B)))) &&
-      match(Op1, m_Xor(m_Specific(A), m_Specific(B))))
+  // (A & ~B) | (B ^ A) -> (B ^ A)
+  // (~B & A) | (B ^ A) -> (B ^ A)
+  if (match(Op1, m_Xor(m_Value(A), m_Value(B))) &&
+      (match(Op0, m_c_And(m_Specific(A), m_Not(m_Specific(B)))) ||
+       match(Op0, m_c_And(m_Not(m_Specific(A)), m_Specific(B)))))
     return Op1;
 
   // Commute the 'or' operands.
   // (A ^ B) | (A & ~B) -> (A ^ B)
   // (A ^ B) | (~B & A) -> (A ^ B)
-  if (match(Op1, m_c_And(m_Value(A), m_Not(m_Value(B)))) &&
-      match(Op0, m_Xor(m_Specific(A), m_Specific(B))))
+  // (B ^ A) | (A & ~B) -> (B ^ A)
+  // (B ^ A) | (~B & A) -> (B ^ A)
+  if (match(Op0, m_Xor(m_Value(A), m_Value(B))) &&
+      (match(Op1, m_c_And(m_Specific(A), m_Not(m_Specific(B)))) ||
+       match(Op1, m_c_And(m_Not(m_Specific(A)), m_Specific(B)))))
     return Op0;
 
   if (auto *ICILHS = dyn_cast<ICmpInst>(Op0)) {
diff --git a/llvm/test/Transforms/InstSimplify/AndOrXor.ll b/llvm/test/Transforms/InstSimplify/AndOrXor.ll
index 5292732842b..c5108217056 100644
--- a/llvm/test/Transforms/InstSimplify/AndOrXor.ll
+++ b/llvm/test/Transforms/InstSimplify/AndOrXor.ll
@@ -521,3 +521,65 @@ define i32 @test44_commuted_and(i32 %a, i32 %b) {
   ret i32 %or
 }
 
+; (~A & ~B) | (~A ^ B) -> ~A ^ B
+
+define i32 @test45(i32 %a, i32 %b) {
+; CHECK-LABEL: @test45(
+; CHECK-NEXT:    [[NEGB:%.*]] = xor i32 [[B:%.*]], -1
+; CHECK-NEXT:    [[XOR:%.*]] = xor i32 [[A:%.*]], [[NEGB]]
+; CHECK-NEXT:    ret i32 [[XOR]]
+;
+  %nega = xor i32 %a, -1
+  %negb = xor i32 %b, -1
+  %and = and i32 %nega, %negb
+  %xor = xor i32 %a, %negb
+  %or = or i32 %and, %xor
+  ret i32 %or
+}
+
+define i32 @test45_commuted_and(i32 %a, i32 %b) {
+; CHECK-LABEL: @test45(
+; CHECK-NEXT:    [[NEGB:%.*]] = xor i32 [[B:%.*]], -1
+; CHECK-NEXT:    [[XOR:%.*]] = xor i32 [[A:%.*]], [[NEGB]]
+; CHECK-NEXT:    ret i32 [[XOR]]
+;
+  %nega = xor i32 %a, -1
+  %negb = xor i32 %b, -1
+  %and = and i32 %negb, %nega
+  %xor = xor i32 %a, %negb
+  %or = or i32 %and, %xor
+  ret i32 %or
+}
+
+; Commute operands of the 'or'.
+; (~A ^ B) | (~A & ~B) -> ~A ^ B
+
+define i32 @test46(i32 %a, i32 %b) {
+; CHECK-LABEL: @test46(
+; CHECK-NEXT:    [[NEGB:%.*]] = xor i32 [[B:%.*]], -1
+; CHECK-NEXT:    [[XOR:%.*]] = xor i32 [[A:%.*]], [[NEGB]]
+; CHECK-NEXT:    ret i32 [[XOR]]
+;
+  %nega = xor i32 %a, -1
+  %negb = xor i32 %b, -1
+  %and = and i32 %nega, %negb
+  %xor = xor i32 %a, %negb
+  %or = or i32 %xor, %and
+  ret i32 %or
+}
+
+; (~A & ~B) | (~A ^ B) -> ~A ^ B
+
+define i32 @test46_commuted_and(i32 %a, i32 %b) {
+; CHECK-LABEL: @test45(
+; CHECK-NEXT:    [[NEGB:%.*]] = xor i32 [[B:%.*]], -1
+; CHECK-NEXT:    [[XOR:%.*]] = xor i32 [[A:%.*]], [[NEGB]]
+; CHECK-NEXT:    ret i32 [[XOR]]
+;
+  %nega = xor i32 %a, -1
+  %negb = xor i32 %b, -1
+  %and = and i32 %negb, %nega
+  %xor = xor i32 %a, %negb
+  %or = or i32 %xor, %and
+  ret i32 %or
+}