[llvm] 79011c7 - [InstCombine] Fix rare condition violation in canonicalizeClampLike

[David Green via llvm-commits]

Author: David Green
Date: 2021-10-28T15:03:07+01:00
New Revision: 79011c705b5849661cc791016c54ee62d9ec9cb0

URL: https://github.com/llvm/llvm-project/commit/79011c705b5849661cc791016c54ee62d9ec9cb0
DIFF: https://github.com/llvm/llvm-project/commit/79011c705b5849661cc791016c54ee62d9ec9cb0.diff

LOG: [InstCombine] Fix rare condition violation in canonicalizeClampLike

With a "ult x, 0", the fold in canonicalizeClampLike does not validate
with undef inputs. This condition will usually have been simplified
away, but we should ensure the code is correct in case.
https://alive2.llvm.org/ce/z/S8HQ6H vs https://alive2.llvm.org/ce/z/h2XBJ_

See: https://reviews.llvm.org/D108049

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
    llvm/test/Transforms/InstCombine/truncating-saturate.ll

Removed: 
    


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diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index 15309543870b..586be591c9b7 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -1307,6 +1307,13 @@ static Instruction *canonicalizeClampLike(SelectInst &Sel0, ICmpInst &Cmp0,
   // FIXME: we shouldn't care about lanes that are 'undef' in the end?
   switch (Cmp0.getPredicate()) {
   case ICmpInst::Predicate::ICMP_ULT:
+    // Although icmp ult %x, 0 is an unusual thing to try and should generally
+    // have been simplified, it does not verify with undef inputs so ensure we
+    // are not in a strange state.
+    if (!match(C0, m_SpecificInt_ICMP(
+                       ICmpInst::Predicate::ICMP_NE,
+                       APInt::getZero(C0->getType()->getScalarSizeInBits()))))
+      return nullptr;
     break; // Great!
   case ICmpInst::Predicate::ICMP_ULE:
     // We'd have to increment C0 by one, and for that it must not have all-ones

diff  --git a/llvm/test/Transforms/InstCombine/truncating-saturate.ll b/llvm/test/Transforms/InstCombine/truncating-saturate.ll
index 06d2c208fd28..c77fb68eebc1 100644
--- a/llvm/test/Transforms/InstCombine/truncating-saturate.ll
+++ b/llvm/test/Transforms/InstCombine/truncating-saturate.ll
@@ -600,10 +600,11 @@ define <2 x i8> @C0zeroV(<2 x i8> %X, <2 x i8> %y, <2 x i8> %z) {
 
 define <2 x i8> @C0zeroVu(<2 x i8> %X, <2 x i8> %y, <2 x i8> %z) {
 ; CHECK-LABEL: @C0zeroVu(
-; CHECK-NEXT:    [[TMP1:%.*]] = icmp slt <2 x i8> [[X:%.*]], <i8 -10, i8 -10>
-; CHECK-NEXT:    [[TMP2:%.*]] = icmp sgt <2 x i8> [[X]], <i8 -11, i8 -1>
-; CHECK-NEXT:    [[TMP3:%.*]] = select <2 x i1> [[TMP1]], <2 x i8> [[Y:%.*]], <2 x i8> [[X]]
-; CHECK-NEXT:    [[R:%.*]] = select <2 x i1> [[TMP2]], <2 x i8> [[Z:%.*]], <2 x i8> [[TMP3]]
+; CHECK-NEXT:    [[A:%.*]] = add <2 x i8> [[X:%.*]], <i8 10, i8 10>
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ult <2 x i8> [[A]], <i8 0, i8 10>
+; CHECK-NEXT:    [[C:%.*]] = icmp slt <2 x i8> [[X]], <i8 -10, i8 -10>
+; CHECK-NEXT:    [[F:%.*]] = select <2 x i1> [[C]], <2 x i8> [[Y:%.*]], <2 x i8> [[Z:%.*]]
+; CHECK-NEXT:    [[R:%.*]] = select <2 x i1> [[CMP]], <2 x i8> [[X]], <2 x i8> [[F]]
 ; CHECK-NEXT:    ret <2 x i8> [[R]]
 ;
   %a = add <2 x i8> %X, <i8 10, i8 10>