[llvm] 1f8ac37 - [InstCombine] adjust branch on logical-and fold

[Sanjay Patel via llvm-commits]

Author: Sanjay Patel
Date: 2022-10-31T17:39:29-04:00
New Revision: 1f8ac37e2d50b0175225a0d8f3f5003f64b46b89

URL: https://github.com/llvm/llvm-project/commit/1f8ac37e2d50b0175225a0d8f3f5003f64b46b89
DIFF: https://github.com/llvm/llvm-project/commit/1f8ac37e2d50b0175225a0d8f3f5003f64b46b89.diff

LOG: [InstCombine] adjust branch on logical-and fold

The transform was just added with:
115d2f69a515cd756fa51
...but as noted in post-commit feedback, it was
confusingly coded. Now, we create the final
expected canonicalized form directly and put
an extra use check on the match, so we should
not ever end up with more instructions.

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
    llvm/test/Transforms/InstCombine/branch.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index 4459e16c224d..ba51ee5c4440 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -3187,13 +3187,17 @@ Instruction *InstCombinerImpl::visitBranchInst(BranchInst &BI) {
     return replaceOperand(BI, 0, X);
   }
 
-  // br (X && !Y), T, F --> br ((X && Y) || !X), F, T
+  // Canonicalize logical-and-with-invert as logical-or-with-invert.
+  // This is done by inverting the condition and swapping successors:
+  // br (X && !Y), T, F --> br !(X && !Y), F, T --> br (!X || Y), F, T
   Value *Y;
   if (isa<SelectInst>(Cond) &&
-      match(Cond, m_OneUse(m_LogicalAnd(m_Value(X), m_Not(m_Value(Y)))))) {
-    Value *AndOr = Builder.CreateSelect(X, Y, Builder.getTrue());
+      match(Cond,
+            m_OneUse(m_LogicalAnd(m_Value(X), m_OneUse(m_Not(m_Value(Y))))))) {
+    Value *NotX = Builder.CreateNot(X, "not." + X->getName());
+    Value *Or = Builder.CreateLogicalOr(NotX, Y);
     BI.swapSuccessors();
-    return replaceOperand(BI, 0, AndOr);
+    return replaceOperand(BI, 0, Or);
   }
 
   // If the condition is irrelevant, remove the use so that other

diff  --git a/llvm/test/Transforms/InstCombine/branch.ll b/llvm/test/Transforms/InstCombine/branch.ll
index 2961dec50adf..1110d5f90b17 100644
--- a/llvm/test/Transforms/InstCombine/branch.ll
+++ b/llvm/test/Transforms/InstCombine/branch.ll
@@ -189,14 +189,15 @@ f:
   ret i32 3
 }
 
+; negative test
+
 define i32 @logical_and_not_use1(i1 %x, i1 %y) {
 ; CHECK-LABEL: @logical_and_not_use1(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[NOTY:%.*]] = xor i1 [[Y:%.*]], true
 ; CHECK-NEXT:    call void @use(i1 [[NOTY]])
-; CHECK-NEXT:    [[NOT_X:%.*]] = xor i1 [[X:%.*]], true
-; CHECK-NEXT:    [[TMP0:%.*]] = select i1 [[NOT_X]], i1 true, i1 [[Y]]
-; CHECK-NEXT:    br i1 [[TMP0]], label [[F:%.*]], label [[T:%.*]]
+; CHECK-NEXT:    [[AND:%.*]] = select i1 [[X:%.*]], i1 [[NOTY]], i1 false
+; CHECK-NEXT:    br i1 [[AND]], label [[T:%.*]], label [[F:%.*]]
 ; CHECK:       t:
 ; CHECK-NEXT:    ret i32 42
 ; CHECK:       f: