[llvm] 16e2ec8 - [ValueTracking] Make undef element check more precise

[Nikita Popov via llvm-commits]

Author: Nikita Popov
Date: 2024-06-06T09:39:33+02:00
New Revision: 16e2ec82ac45701f9c55ab917e30f38dbae6f79a

URL: https://github.com/llvm/llvm-project/commit/16e2ec82ac45701f9c55ab917e30f38dbae6f79a
DIFF: https://github.com/llvm/llvm-project/commit/16e2ec82ac45701f9c55ab917e30f38dbae6f79a.diff

LOG: [ValueTracking] Make undef element check more precise

If we're only checking for undef, then also only look for undef
elements in the vector (rather than undef and poison).

Added: 
    

Modified: 
    llvm/lib/Analysis/ValueTracking.cpp
    llvm/test/Transforms/InstCombine/select.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index 08138a5e2f2d9..782c28c944837 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -7296,10 +7296,13 @@ static bool isGuaranteedNotToBeUndefOrPoison(
         isa<ConstantPointerNull>(C) || isa<Function>(C))
       return true;
 
-    if (C->getType()->isVectorTy() && !isa<ConstantExpr>(C))
-      return (!includesUndef(Kind) ? !C->containsPoisonElement()
-                                   : !C->containsUndefOrPoisonElement()) &&
-             !C->containsConstantExpression();
+    if (C->getType()->isVectorTy() && !isa<ConstantExpr>(C)) {
+      if (includesUndef(Kind) && C->containsUndefElement())
+        return false;
+      if (includesPoison(Kind) && C->containsPoisonElement())
+        return false;
+      return !C->containsConstantExpression();
+    }
   }
 
   // Strip cast operations from a pointer value.

diff  --git a/llvm/test/Transforms/InstCombine/select.ll b/llvm/test/Transforms/InstCombine/select.ll
index 29b4d602ffa02..a0ee4383495cc 100644
--- a/llvm/test/Transforms/InstCombine/select.ll
+++ b/llvm/test/Transforms/InstCombine/select.ll
@@ -2787,8 +2787,7 @@ define <2 x i8> @select_replacement_add_eq_vec_nonuniform(<2 x i8> %x, <2 x i8>
 define <2 x i8> @select_replacement_add_eq_vec_poison(<2 x i8> %x, <2 x i8> %y) {
 ; CHECK-LABEL: @select_replacement_add_eq_vec_poison(
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp eq <2 x i8> [[X:%.*]], <i8 1, i8 poison>
-; CHECK-NEXT:    [[ADD:%.*]] = add <2 x i8> [[X]], <i8 1, i8 1>
-; CHECK-NEXT:    [[SEL:%.*]] = select <2 x i1> [[CMP]], <2 x i8> [[ADD]], <2 x i8> [[Y:%.*]]
+; CHECK-NEXT:    [[SEL:%.*]] = select <2 x i1> [[CMP]], <2 x i8> <i8 2, i8 poison>, <2 x i8> [[Y:%.*]]
 ; CHECK-NEXT:    ret <2 x i8> [[SEL]]
 ;
   %cmp = icmp eq <2 x i8> %x, <i8 1, i8 poison>