[llvm] [ArgPromotion] Handle pointer arguments of recursive calls (PR #78735)

[Vedant Paranjape via llvm-commits]

================
@@ -422,13 +422,16 @@ doPromotion(Function *F, FunctionAnalysisManager &FAM,
 
 /// Return true if we can prove that all callees pass in a valid pointer for the
 /// specified function argument.
-static bool allCallersPassValidPointerForArgument(Argument *Arg,
-                                                  Align NeededAlign,
-                                                  uint64_t NeededDerefBytes) {
+static bool allCallersPassValidPointerForArgument(
+    Argument *Arg, SmallPtrSet<CallBase *, 4> &RecursiveCalls,
+    Align NeededAlign, uint64_t NeededDerefBytes) {
   Function *Callee = Arg->getParent();
   const DataLayout &DL = Callee->getParent()->getDataLayout();
   APInt Bytes(64, NeededDerefBytes);
 
+  if (RecursiveCalls.size())
+    return true;
----------------
vedantparanjape-amd wrote:

> > Do, you suggest I add the !dereferenceable metadata to this and run the testcase ?
> 
> I was thinking a dereferenceable attribute, not metadata. But yes, that probably makes sense.

```
define internal i32 @foo(ptr dereferenceable(16) %x, i32 %n, i32 %m) {
entry:
  %tmp = icmp ne i32 %n, 0
  br i1 %tmp, label %cond_true, label %cond_false

cond_true:                                        ; preds = %entry
  %tmp2 = load i32, ptr %x, align 4
  br label %return

cond_false:                                       ; preds = %entry
  %tmp5 = load i32, ptr %x, align 4
  %tmp7 = sub i32 %n, 1
  %tmp9 = call i32 @foo(ptr %x, i32 %tmp7, i32 %tmp5)
  %tmp11 = sub i32 %n, 2
  %tmp14 = call i32 @foo(ptr %x, i32 %tmp11, i32 %m)
  %tmp15 = add i32 %tmp9, %tmp14
  br label %return

cond_next:                                        ; No predecessors!
  br label %return

return:                                           ; preds = %cond_next, %cond_false, %cond_true
  %retval.0 = phi i32 [ %tmp2, %cond_true ], [ %tmp15, %cond_false ], [ undef, %cond_next ]
  ret i32 %retval.0
}

define i32 @bar(ptr %x, i32 %n, i32 %m) {
entry:
  %load0 = load i32, ptr %x, align 4
  %tmp3 = call i32 @foo(ptr %x, i32 %n, i32 %m)
  br label %return

return:                                           ; preds = %entry
  ret i32 %tmp3
}
``` 
I tried something like this, doesn't seem to work either! Can you take a look what might be wrong ?

> > can this be a part of a separate patch
> 
> Sure.



https://github.com/llvm/llvm-project/pull/78735