[SROA] Fix PR32902 by more carefully propagating !nonnull metadata.

This is based heavily on the work done ni D34285. I mostly wanted to do
test cleanup for the author to save them some time, but I had a really
hard time understanding why it was so hard to write better test cases
for these issues.

The problem is that because SROA does a second rewrite of the loads and
because we *don't* propagate !nonnull for non-pointer loads, we first
introduced invalid !nonnull metadata and then stripped it back off just
in time to avoid most ways of this PR manifesting. Moving to the more
careful utility only fixes this by changing the predicate to look at the
new load's type rather than the target type. However, that *does* fix
the bug, and the utility is much nicer including adding range metadata
to model the nonnull property after a conversion to an integer.

However, we have bigger problems because we don't actually propagate
*range* metadata, and the utility to do this extracted from instcombine
isn't really in good shape to do this currently. It *only* handles the
case of copying range metadata from an integer load to a pointer load.
It doesn't even handle the trivial cases of propagating from one integer
load to another when they are the same width! This utility will need to
be beefed up prior to using in this location to get the metadata to
fully survive.

And even then, we need to go and teach things to turn the range metadata
into an assume the way we do with nonnull so that when we *promote* an
integer we don't lose the information.

All of this will require a new test case that looks kind-of like
`preserve-nonnull.ll` does here but focuses on range metadata. It will
also likely require more testing because it needs to correctly handle
changes to the integer width, especially as SROA actively tries to
change the integer width!

Last but not least, I'm a little worried about hooking the range
metadata up here because the instcombine logic for converting from
a range metadata *to* a nonnull metadata node seems broken in the face
of non-zero address spaces where null is not mapped to the integer `0`.
So that probably needs to get fixed with test cases both in SROA and in
instcombine to cover it.

But this *does* extract the core PR fix from D34285 of preventing the
!nonnull metadata from being propagated in a broken state just long
enough to feed into promotion and crash value tracking.

On D34285 there is some discussion of zero-extend handling because it
isn't necessary. First, the new load size covers all of the non-undef
(ie, possibly initialized) bits. This may even extend past the original
alloca if loading those bits could produce valid data. The only way its
valid for us to zero-extend an integer load in SROA is if the original
code had a zero extend or those bits were undef. And we get to assume
things like undef *never* satifies nonnull, so non undef bits can
participate here. No need to special case the zero-extend handling, it
just falls out correctly.

The original credit goes to Ariel Ben-Yehuda! I'm mostly landing this to
save a few rounds of trivial edits fixing style issues and test case
formulation.

Differental Revision: D34285

llvm-svn: 306379

lib/Transforms/Scalar/SROA.cpp

@@ -2402,9 +2402,20 @@ private:
       if (LI.isVolatile())
         NewLI->setAtomic(LI.getOrdering(), LI.getSynchScope());
 
+      // Any !nonnull metadata or !range metadata on the old load is also valid
+      // on the new load. This is even true in some cases even when the loads
+      // are different types, for example by mapping !nonnull metadata to
+      // !range metadata by modeling the null pointer constant converted to the
+      // integer type.
+      // FIXME: Add support for range metadata here. Currently the utilities
+      // for this don't propagate range metadata in trivial cases from one
+      // integer load to another, don't handle non-addrspace-0 null pointers
+      // correctly, and don't have any support for mapping ranges as the
+      // integer type becomes winder or narrower.
+      if (MDNode *N = LI.getMetadata(LLVMContext::MD_nonnull))
+        copyNonnullMetadata(LI, N, *NewLI);
+
       // Try to preserve nonnull metadata
-      if (TargetTy->isPointerTy())
-        NewLI->copyMetadata(LI, LLVMContext::MD_nonnull);
       V = NewLI;
 
       // If this is an integer load past the end of the slice (which means the

test/Transforms/SROA/preserve-nonnull.ll

@@ -42,4 +42,51 @@ entry:
   ret float* %ret
 }
 
+; Make sure we properly handle the !nonnull attribute when we convert
+; a pointer load to an integer load.
+; FIXME: While this doesn't do anythnig actively harmful today, it really
+; should propagate the !nonnull metadata to range metadata. The irony is, it
+; *does* initially, but then we lose that !range metadata before we finish
+; SROA.
+define i8* @propagate_nonnull_to_int() {
+; CHECK-LABEL: define i8* @propagate_nonnull_to_int(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    %[[A:.*]] = alloca i64
+; CHECK-NEXT:    store i64 42, i64* %[[A]]
+; CHECK-NEXT:    %[[LOAD:.*]] = load volatile i64, i64* %[[A]]
+; CHECK-NEXT:    %[[CAST:.*]] = inttoptr i64 %[[LOAD]] to i8*
+; CHECK-NEXT:    ret i8* %[[CAST]]
+entry:
+  %a = alloca [2 x i8*]
+  %a.gep0 = getelementptr [2 x i8*], [2 x i8*]* %a, i32 0, i32 0
+  %a.gep1 = getelementptr [2 x i8*], [2 x i8*]* %a, i32 0, i32 1
+  %a.gep0.cast = bitcast i8** %a.gep0 to i64*
+  %a.gep1.cast = bitcast i8** %a.gep1 to i64*
+  store i64 42, i64* %a.gep1.cast
+  store i64 0, i64* %a.gep0.cast
+  %load = load volatile i8*, i8** %a.gep1, !nonnull !0
+  ret i8* %load
+}
+
+; Make sure we properly handle the !nonnull attribute when we convert
+; a pointer load to an integer load and immediately promote it to an SSA
+; register. This can fail in interesting ways due to the rewrite iteration of
+; SROA, resulting in PR32902.
+define i8* @propagate_nonnull_to_int_and_promote() {
+; CHECK-LABEL: define i8* @propagate_nonnull_to_int_and_promote(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    %[[PROMOTED_VALUE:.*]] = inttoptr i64 42 to i8*
+; CHECK-NEXT:    ret i8* %[[PROMOTED_VALUE]]
+entry:
+  %a = alloca [2 x i8*], align 8
+  %a.gep0 = getelementptr [2 x i8*], [2 x i8*]* %a, i32 0, i32 0
+  %a.gep1 = getelementptr [2 x i8*], [2 x i8*]* %a, i32 0, i32 1
+  %a.gep0.cast = bitcast i8** %a.gep0 to i64*
+  %a.gep1.cast = bitcast i8** %a.gep1 to i64*
+  store i64 42, i64* %a.gep1.cast
+  store i64 0, i64* %a.gep0.cast
+  %load = load i8*, i8** %a.gep1, align 8, !nonnull !0
+  ret i8* %load
+}
+
 !0 = !{}