[llvm] d8b2686 - [InstCombine] prevent infinite looping in or-icmp fold (PR46712)

[Sanjay Patel via llvm-commits]

Author: Sanjay Patel
Date: 2020-07-15T14:12:12-04:00
New Revision: d8b268680d0858aaf30cb1a278b64b11361bc780

URL: https://github.com/llvm/llvm-project/commit/d8b268680d0858aaf30cb1a278b64b11361bc780
DIFF: https://github.com/llvm/llvm-project/commit/d8b268680d0858aaf30cb1a278b64b11361bc780.diff

LOG: [InstCombine] prevent infinite looping in or-icmp fold (PR46712)

I'm not sure if the test is truly minimal, but we need to
induce a situation where a value becomes a constant but is
not immediately folded before getting to the 'or' transform.

Added: 
    

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

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index d3c718a919c0..1304d46fdef4 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -1148,11 +1148,12 @@ static Value *foldAndOrOfICmpsWithConstEq(ICmpInst *Cmp0, ICmpInst *Cmp1,
   assert((IsAnd || Logic.getOpcode() == Instruction::Or) && "Wrong logic op");
 
   // Match an equality compare with a non-poison constant as Cmp0.
+  // Also, give up if the compare can be constant-folded to avoid looping.
   ICmpInst::Predicate Pred0;
   Value *X;
   Constant *C;
   if (!match(Cmp0, m_ICmp(Pred0, m_Value(X), m_Constant(C))) ||
-      !isGuaranteedNotToBeUndefOrPoison(C))
+      !isGuaranteedNotToBeUndefOrPoison(C) || isa<Constant>(X))
     return nullptr;
   if ((IsAnd && Pred0 != ICmpInst::ICMP_EQ) ||
       (!IsAnd && Pred0 != ICmpInst::ICMP_NE))

diff  --git a/llvm/test/Transforms/InstCombine/or.ll b/llvm/test/Transforms/InstCombine/or.ll
index b747c5d97810..48496948c190 100644
--- a/llvm/test/Transforms/InstCombine/or.ll
+++ b/llvm/test/Transforms/InstCombine/or.ll
@@ -841,3 +841,38 @@ define <16 x i1> @test51(<16 x i1> %arg, <16 x i1> %arg1) {
   %tmp3 = or <16 x i1> %tmp, %tmp2
   ret <16 x i1> %tmp3
 }
+
+; This would infinite loop because it reaches a transform
+; that was not expecting a constant-foldable value.
+
+define i32 @PR46712(i1 %x, i1 %y, i1 %b, i64 %z) {
+; CHECK-LABEL: @PR46712(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br i1 [[B:%.*]], label [[TRUE:%.*]], label [[END:%.*]]
+; CHECK:       true:
+; CHECK-NEXT:    [[BOOL5:%.*]] = icmp eq i64 [[Z:%.*]], 0
+; CHECK-NEXT:    [[SEL:%.*]] = zext i1 [[BOOL5]] to i32
+; CHECK-NEXT:    br label [[END]]
+; CHECK:       end:
+; CHECK-NEXT:    [[T5:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[SEL]], [[TRUE]] ]
+; CHECK-NEXT:    ret i32 [[T5]]
+;
+entry:
+  %t2 = or i1 %x, %y
+  %conv = sext i1 %t2 to i32
+  %cmp = icmp sge i32 %conv, 1
+  %conv2 = zext i1 %cmp to i64
+  br i1 %b, label %true, label %end
+
+true:
+  %bool4 = icmp eq i64 %conv2, 0
+  %bool5 = icmp ne i64 %z, 0
+  %and = and i1 %bool4, %bool5
+  %sel = select i1 %and, i1 false, i1 true
+  br label %end
+
+end:
+  %t5 = phi i1 [ 0, %entry ], [ %sel, %true ]
+  %conv8 = zext i1 %t5 to i32
+  ret i32 %conv8
+}