[PATCH] D100445: [RS4GC] Introduce intrinsics to get base ptr and offset

[Yevgeny Rouban via Phabricator via llvm-commits]

yrouban marked 5 inline comments as done.
yrouban added a comment.

I'm still working on the next version.



================
Comment at: llvm/lib/Transforms/Scalar/RewriteStatepointsForGC.cpp:599
 
+  // This value might have been generated by findBasePointer() called when
+  // substituting gc.get.pointer.base() intrinsic.
----------------
reames wrote:
> I don't think this piece of the change should be required.  Can you explain why this is needed?
This case is tested in the new intrinsics.ll:

Here is a simplified version:
```
define void @test_chained(i8 addrspace(1)* %obj1, i8 addrspace(1)* %obj2, i32 %len, i1 %c) gc "statepoint-example" {
entry:
  %obj1.12 = getelementptr inbounds i8, i8 addrspace(1)* %obj1, i64 12
  %obj2.16 = getelementptr inbounds i8, i8 addrspace(1)* %obj2, i64 16
  %obj.x = select i1 %c, i8 addrspace(1)* %obj1.12, i8 addrspace(1)* %obj2.16

  %obj.x.base = call i8 addrspace(1)* @llvm.experimental.gc.get.pointer.base.p1i8.p1i8(i8 addrspace(1)* %obj.x)
  %obj.x.base_of_base = call i8 addrspace(1)* @llvm.experimental.gc.get.pointer.base.p1i8.p1i8(i8 addrspace(1)* %obj.x.base)

  ret void
}

```
After the first //%obj.x.base = get.pointer.base(%obj.x)// is inlined by //inlineGetBaseAndOffset()// we get all //%obj.x.base// uses RAUWed with the result //%obj.x.base1// which is marked with !is_base_value:
```
  %obj1.12 = getelementptr inbounds i8, i8 addrspace(1)* %obj1, i64 12
  %obj2.16 = getelementptr inbounds i8, i8 addrspace(1)* %obj2, i64 16
  %obj.x.base1 = select i1 %c, i8 addrspace(1)* %obj1, i8 addrspace(1)* %obj2, !is_base_value !0
  %obj.x = select i1 %c, i8 addrspace(1)* %obj1.12, i8 addrspace(1)* %obj2.16
  %obj.x.base_of_base = call i8 addrspace(1)* @llvm.experimental.gc.get.pointer.base.p1i8.p1i8(i8 addrspace(1)* %obj.x.base1)
```
Then //inlineGetBaseAndOffset()// calls //findBasePointer(%obj.x.base1)//, which ends up in instantiating //BaseDefiningValueResult(%obj.x.base1, IsKnownBase)//.


Repository:
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  https://reviews.llvm.org/D100445/new/

https://reviews.llvm.org/D100445