[AssumptionCache] Do not track llvm.assume calls (PR49043)

[jdoerfert]

Summary

This fixes PR49043 by invalidating the handle on RAUW. This will work
fine assuming all existing RAUW users add the new assumption to the
cache. That means, if a new llvm.assume call replaces an old one, you
need to add the new one now as a RAUW is not enough anymore.

[nikic]

LGTM as well. I'm okay with either this one or D96168. This is a direct fix for the bug, while D96168 is more an improvement to avoid keeping nulled-out value handles around in the cache.

[jdoerfert]

In D96208#2546963, @nikic wrote:

LGTM as well. I'm okay with either this one or D96168. This is a direct fix for the bug, while D96168 is more an improvement to avoid keeping nulled-out value handles around in the cache.

I'll do one after the other.If there is ever a compile time or other problem we can revisit the self updating set but don't run into this again.

llvm/include/llvm/Analysis/AssumptionCache.h

 /// \@llvm.assume calls do not require special handling.
 class AssumptionCache {
 public:
   /// Value of ResultElem::Index indicating that the argument to the call of the
   /// llvm.assume.
   enum : unsigned { ExprResultIdx = std::numeric_limits<unsigned>::max() };
 
   struct ResultElem {
-    WeakTrackingVH Assume;
+    WeakVH Assume;
 
     /// contains either ExprResultIdx or the index of the operand bundle
     /// containing the knowledge.
     unsigned Index;
     operator Value *() const { return Assume; }
   };
 
 private:

llvm/test/Transforms/GVNSink/assumption.ll

+; RUN: opt < %s -S -passes="print<assumptions>,gvn-sink,loop-unroll" -unroll-count=3 | FileCheck %s
+;
+; This crashed because the cached assumption was replaced and the replacement
+; was then in the cache twice.
+;
+; PR49043
+
+@g = external global i32
+
+define void @main() {
+bb:
+  %i1.i = load volatile i32, i32* @g
+  %i32.i = icmp eq i32 %i1.i, 0
+  call void @llvm.assume(i1 %i32.i) #3
+  br label %bb4.i
+
+bb4.i:                                            ; preds = %bb4.i, %bb
+  %i.i = load volatile i32, i32* @g
+  %i3.i = icmp eq i32 %i.i, 0
+  call void @llvm.assume(i1 %i3.i) #3
+  br label %bb4.i
+
+func_1.exit:                                      ; No predecessors!
+  unreachable
+}
+
+declare void @llvm.assume(i1)
+
+; CHECK:  call void @llvm.assume(
+; CHECK:  call void @llvm.assume(
+; CHECK:  call void @llvm.assume(
+