[llvm] 8a6698b - [ValueTracking] Loads with !dereferenceable metadata cannot be undef/poison

[Nikita Popov via llvm-commits]

Author: Nikita Popov
Date: 2022-05-25T09:54:04+02:00
New Revision: 8a6698b5238228876e7e5eb20ed82167ab1b04db

URL: https://github.com/llvm/llvm-project/commit/8a6698b5238228876e7e5eb20ed82167ab1b04db
DIFF: https://github.com/llvm/llvm-project/commit/8a6698b5238228876e7e5eb20ed82167ab1b04db.diff

LOG: [ValueTracking] Loads with !dereferenceable metadata cannot be undef/poison

A load with !dereferenceable or !dereferenceable_or_null metadata
must return a well-defined (non-undef/poison) value. Effectively
they imply !noundef. This is the same as we do for the
dereferenceable(N) attribute.

This should fix https://github.com/llvm/llvm-project/issues/55672,
or at least the specific case discussed there.

Differential Revision: https://reviews.llvm.org/D126296

Added: 
    

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

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Analysis/ValueTracking.cpp b/llvm/lib/Analysis/ValueTracking.cpp
index a32633589c94a..c7586f271df10 100644
--- a/llvm/lib/Analysis/ValueTracking.cpp
+++ b/llvm/lib/Analysis/ValueTracking.cpp
@@ -5191,7 +5191,9 @@ static bool isGuaranteedNotToBeUndefOrPoison(const Value *V,
   }
 
   if (auto *I = dyn_cast<LoadInst>(V))
-    if (I->getMetadata(LLVMContext::MD_noundef))
+    if (I->hasMetadata(LLVMContext::MD_noundef) ||
+        I->hasMetadata(LLVMContext::MD_dereferenceable) ||
+        I->hasMetadata(LLVMContext::MD_dereferenceable_or_null))
       return true;
 
   if (programUndefinedIfUndefOrPoison(V, PoisonOnly))

diff  --git a/llvm/test/Transforms/InstCombine/freeze.ll b/llvm/test/Transforms/InstCombine/freeze.ll
index 43b4c4a90e49f..92c1e9a1328b6 100644
--- a/llvm/test/Transforms/InstCombine/freeze.ll
+++ b/llvm/test/Transforms/InstCombine/freeze.ll
@@ -834,8 +834,7 @@ define i8* @freeze_load_noundef(i8** %ptr) {
 define i8* @freeze_load_dereferenceable(i8** %ptr) {
 ; CHECK-LABEL: @freeze_load_dereferenceable(
 ; CHECK-NEXT:    [[P:%.*]] = load i8*, i8** [[PTR:%.*]], align 8, !dereferenceable !1
-; CHECK-NEXT:    [[P_FR:%.*]] = freeze i8* [[P]]
-; CHECK-NEXT:    ret i8* [[P_FR]]
+; CHECK-NEXT:    ret i8* [[P]]
 ;
   %p = load i8*, i8** %ptr, !dereferenceable !1
   %p.fr = freeze i8* %p
@@ -845,8 +844,7 @@ define i8* @freeze_load_dereferenceable(i8** %ptr) {
 define i8* @freeze_load_dereferenceable_or_null(i8** %ptr) {
 ; CHECK-LABEL: @freeze_load_dereferenceable_or_null(
 ; CHECK-NEXT:    [[P:%.*]] = load i8*, i8** [[PTR:%.*]], align 8, !dereferenceable_or_null !1
-; CHECK-NEXT:    [[P_FR:%.*]] = freeze i8* [[P]]
-; CHECK-NEXT:    ret i8* [[P_FR]]
+; CHECK-NEXT:    ret i8* [[P]]
 ;
   %p = load i8*, i8** %ptr, !dereferenceable_or_null !1
   %p.fr = freeze i8* %p