[SROA] Don't shrink volatile load past end

For volatile atomic, this may result in a verifier errors, if the
new alloca type is not legal for atomic accesses.

I've opted to disable this special case for volatile accesses in
general, as changing the size of the volatile access seems
dubious in any case.

Fixes #64721.

Author: nikic

llvm/lib/Transforms/Scalar/SROA.cpp

@@ -2713,7 +2713,7 @@ class llvm::sroa::AllocaSliceRewriter
                NewEndOffset == NewAllocaEndOffset &&
                (canConvertValue(DL, NewAllocaTy, TargetTy) ||
                 (IsLoadPastEnd && NewAllocaTy->isIntegerTy() &&
-                 TargetTy->isIntegerTy()))) {
+                 TargetTy->isIntegerTy() && !LI.isVolatile()))) {
       Value *NewPtr =
           getPtrToNewAI(LI.getPointerAddressSpace(), LI.isVolatile());
       LoadInst *NewLI = IRB.CreateAlignedLoad(NewAI.getAllocatedType(), NewPtr,

llvm/test/Transforms/SROA/basictest.ll

@@ -1968,6 +1968,38 @@ bb7:
   ret void
 }
 
+define i32 @load_atomic_volatile_past_end() {
+; CHECK-LABEL: @load_atomic_volatile_past_end(
+; CHECK-NEXT:    [[A:%.*]] = alloca i1, align 1
+; CHECK-NEXT:    [[A_0_V:%.*]] = load atomic volatile i32, ptr [[A]] seq_cst, align 1
+; CHECK-NEXT:    ret i32 [[A_0_V]]
+;
+  %a = alloca i1, align 1
+  %v = load atomic volatile i32, ptr %a seq_cst, align 4
+  ret i32 %v
+}
+
+define i32 @load_volatile_past_end() {
+; CHECK-LABEL: @load_volatile_past_end(
+; CHECK-NEXT:    [[A:%.*]] = alloca i1, align 1
+; CHECK-NEXT:    [[A_0_V:%.*]] = load volatile i32, ptr [[A]], align 1
+; CHECK-NEXT:    ret i32 [[A_0_V]]
+;
+  %a = alloca i1, align 1
+  %v = load volatile i32, ptr %a, align 4
+  ret i32 %v
+}
+
+define i32 @load_atomic_past_end() {
+; CHECK-LABEL: @load_atomic_past_end(
+; CHECK-NEXT:    [[A_0_LOAD_EXT:%.*]] = zext i1 undef to i32
+; CHECK-NEXT:    ret i32 [[A_0_LOAD_EXT]]
+;
+  %a = alloca i1, align 1
+  %v = load atomic i32, ptr %a seq_cst, align 4
+  ret i32 %v
+}
+
 !0 = !{!1, !1, i64 0, i64 200}
 !1 = !{!2, i64 1, !"type_0"}
 !2 = !{!"root"}