[llvm] r301329 - [InstSimplify] Handle (~A & ~B) | (~A ^ B) -> ~A ^ B

[Craig Topper via llvm-commits]

Author: ctopper
Date: Tue Apr 25 12:01:32 2017
New Revision: 301329

URL: http://llvm.org/viewvc/llvm-project?rev=301329&view=rev
Log:
[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

Modified:
    llvm/trunk/lib/Analysis/InstructionSimplify.cpp
    llvm/trunk/test/Transforms/InstSimplify/AndOrXor.ll

Modified: llvm/trunk/lib/Analysis/InstructionSimplify.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/InstructionSimplify.cpp?rev=301329&r1=301328&r2=301329&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/InstructionSimplify.cpp (original)
+++ llvm/trunk/lib/Analysis/InstructionSimplify.cpp Tue Apr 25 12:01:32 2017
@@ -1886,15 +1886,21 @@ static Value *SimplifyOrInst(Value *Op0,
 
   // (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)) {

Modified: llvm/trunk/test/Transforms/InstSimplify/AndOrXor.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstSimplify/AndOrXor.ll?rev=301329&r1=301328&r2=301329&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstSimplify/AndOrXor.ll (original)
+++ llvm/trunk/test/Transforms/InstSimplify/AndOrXor.ll Tue Apr 25 12:01:32 2017
@@ -521,3 +521,65 @@ define i32 @test44_commuted_and(i32 %a,
   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
+}