[OpenMP][FIX] Properly check assume only uses

We improved our simplification and this exposed a bug in the store
elimination. A load that had dead uses and assume uses was thought to be
used by assumes only. Consequently we also deleted the "dead use users".
This was a problem because a dead use just means we will not use the
load there. The user might still be needed.

Exposed by OvO, reported by @ye-luo.

(cherry picked from commit a51ad87)

Author: jdoerfert

llvm/lib/Transforms/IPO/AttributorAttributes.cpp

@@ -4161,12 +4161,14 @@ struct AAIsDeadFloating : public AAIsDeadValueImpl {
         return true;
       if (auto *LI = dyn_cast<LoadInst>(V)) {
         if (llvm::all_of(LI->uses(), [&](const Use &U) {
-              return InfoCache.isOnlyUsedByAssume(
-                         cast<Instruction>(*U.getUser())) ||
-                     A.isAssumedDead(U, this, nullptr, UsedAssumedInformation);
+              auto &UserI = cast<Instruction>(*U.getUser());
+              if (InfoCache.isOnlyUsedByAssume(UserI)) {
+                if (AssumeOnlyInst)
+                  AssumeOnlyInst->insert(&UserI);
+                return true;
+              }
+              return A.isAssumedDead(U, this, nullptr, UsedAssumedInformation);
             })) {
-          if (AssumeOnlyInst)
-            AssumeOnlyInst->insert(LI);
           return true;
         }
       }

llvm/test/Transforms/Attributor/value-simplify-assume.ll

@@ -390,12 +390,14 @@ define void @assume_2b_nr(i1 %arg, i1 %cond) norecurse {
 ; CHECK: Function Attrs: nofree norecurse nosync nounwind willreturn memory(inaccessiblemem: readwrite)
 ; CHECK-LABEL: define {{[^@]+}}@assume_2b_nr
 ; CHECK-SAME: (i1 [[ARG:%.*]], i1 noundef [[COND:%.*]]) #[[ATTR3]] {
+; CHECK-NEXT:    [[STACK:%.*]] = alloca i1, align 1
 ; CHECK-NEXT:    br i1 [[COND]], label [[T:%.*]], label [[F:%.*]]
 ; CHECK:       t:
 ; CHECK-NEXT:    br label [[M:%.*]]
 ; CHECK:       f:
 ; CHECK-NEXT:    br label [[M]]
 ; CHECK:       m:
+; CHECK-NEXT:    [[L:%.*]] = load i1, ptr [[STACK]], align 1
 ; CHECK-NEXT:    ret void
 ;
   %stack = alloca i1
@@ -1005,12 +1007,14 @@ define void @assume_2b(i1 %arg, i1 %cond) {
 ; CHECK: Function Attrs: nofree norecurse nosync nounwind willreturn memory(inaccessiblemem: readwrite)
 ; CHECK-LABEL: define {{[^@]+}}@assume_2b
 ; CHECK-SAME: (i1 [[ARG:%.*]], i1 noundef [[COND:%.*]]) #[[ATTR3]] {
+; CHECK-NEXT:    [[STACK:%.*]] = alloca i1, align 1
 ; CHECK-NEXT:    br i1 [[COND]], label [[T:%.*]], label [[F:%.*]]
 ; CHECK:       t:
 ; CHECK-NEXT:    br label [[M:%.*]]
 ; CHECK:       f:
 ; CHECK-NEXT:    br label [[M]]
 ; CHECK:       m:
+; CHECK-NEXT:    [[L:%.*]] = load i1, ptr [[STACK]], align 1
 ; CHECK-NEXT:    ret void
 ;
   %stack = alloca i1