[PATCH] D33342: [InstCombine] try to canonicalize xor-of-icmps to and-of-icmps

[Sanjay Patel via Phabricator via llvm-commits]

spatel updated this revision to Diff 101207.
spatel added a comment.

Patch updated:
No code changes, but there was a bug in a code comment that might have caused confusion. Also, updated the 'FIXME' comments in the test file.


https://reviews.llvm.org/D33342

Files:
  lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
  test/Transforms/InstCombine/set.ll


Index: test/Transforms/InstCombine/set.ll
===================================================================
--- test/Transforms/InstCombine/set.ll
+++ test/Transforms/InstCombine/set.ll
@@ -160,29 +160,25 @@
   ret i1 %and
 }
 
-; FIXME: This is equivalent to the previous test.
+; This is equivalent to the previous test.
 
 define i1 @xor_of_icmps(i64 %a) {
 ; CHECK-LABEL: @xor_of_icmps(
-; CHECK-NEXT:    [[B:%.*]] = icmp sgt i64 %a, 0
-; CHECK-NEXT:    [[C:%.*]] = icmp eq i64 %a, 1
-; CHECK-NEXT:    [[XOR:%.*]] = xor i1 [[C]], [[B]]
-; CHECK-NEXT:    ret i1 [[XOR]]
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp sgt i64 %a, 1
+; CHECK-NEXT:    ret i1 [[TMP1]]
 ;
   %b = icmp sgt i64 %a, 0
   %c = icmp eq i64 %a, 1
   %xor = xor i1 %c, %b
   ret i1 %xor
 }
 
-; FIXME: This is also equivalent to the previous test.
+; This is also equivalent to the previous test (commute xor operands).
 
 define i1 @xor_of_icmps_commute(i64 %a) {
 ; CHECK-LABEL: @xor_of_icmps_commute(
-; CHECK-NEXT:    [[B:%.*]] = icmp sgt i64 %a, 0
-; CHECK-NEXT:    [[C:%.*]] = icmp eq i64 %a, 1
-; CHECK-NEXT:    [[XOR:%.*]] = xor i1 [[B]], [[C]]
-; CHECK-NEXT:    ret i1 [[XOR]]
+; CHECK-NEXT:    [[TMP1:%.*]] = icmp sgt i64 %a, 1
+; CHECK-NEXT:    ret i1 [[TMP1]]
 ;
   %b = icmp sgt i64 %a, 0
   %c = icmp eq i64 %a, 1
@@ -209,10 +205,10 @@
 
 define i32 @PR2844(i32 %x) {
 ; CHECK-LABEL: @PR2844(
-; CHECK-NEXT:    [[A:%.*]] = icmp eq i32 %x, 0
+; CHECK-NEXT:    [[A:%.*]] = icmp ne i32 %x, 0
 ; CHECK-NEXT:    [[B:%.*]] = icmp sgt i32 %x, -638208502
-; CHECK-NEXT:    [[NOT_OR:%.*]] = xor i1 [[A]], [[B]]
-; CHECK-NEXT:    [[SEL:%.*]] = zext i1 [[NOT_OR]] to i32
+; CHECK-NEXT:    [[TMP1:%.*]] = and i1 [[A]], [[B]]
+; CHECK-NEXT:    [[SEL:%.*]] = zext i1 [[TMP1]] to i32
 ; CHECK-NEXT:    ret i32 [[SEL]]
 ;
   %A = icmp eq i32 %x, 0
Index: lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -2331,6 +2331,30 @@
     }
   }
 
+  // Instead of trying to imitate the folds for and/or, decompose this 'xor'
+  // into those logic ops and try to turn this into an and-of-icmps because we
+  // have many folds for that pattern.
+  //
+  // This is based on a truth table definition of xor:
+  // X ^ Y --> (X | Y) & !(X & Y)
+  if (Value *OrICmp = SimplifyBinOp(Instruction::Or, LHS, RHS, SQ)) {
+    // TODO: If OrICmp is true, then the definition of xor simplifies to !(X&Y).
+    // TODO: If OrICmp is false, the whole thing is false (InstSimplify?).
+    if (Value *AndICmp = SimplifyBinOp(Instruction::And, LHS, RHS, SQ)) {
+      // TODO: Independently handle cases where the 'and' side is a constant.
+      if (OrICmp == LHS && AndICmp == RHS && RHS->hasOneUse()) {
+        // (LHS | RHS) & !(LHS & RHS) --> LHS & !RHS
+        RHS->setPredicate(RHS->getInversePredicate());
+        return Builder->CreateAnd(LHS, RHS);
+      }
+      if (OrICmp == RHS && AndICmp == LHS && LHS->hasOneUse()) {
+        // !(LHS & RHS) & (LHS | RHS) --> !LHS & RHS
+        LHS->setPredicate(LHS->getInversePredicate());
+        return Builder->CreateAnd(LHS, RHS);
+      }
+    }
+  }
+
   return nullptr;
 }
 


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D33342.101207.patch
Type: text/x-patch
Size: 3266 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20170602/415f5f77/attachment.bin>