[PATCH] D95262: [LLD][PowerPC] Fix bug in PC-Relative initial exec

[Nemanja Ivanovic via Phabricator via llvm-commits]

nemanjai added inline comments.


================
Comment at: lld/test/ELF/ppc64-tls-pcrel-ie.s:82
+# LE-LABEL: <IEAddrCopy>:
+# LE-NEXT:    paddi 3, 13, -28672, 0
+# LE-NEXT:    mr 4, 3
----------------
MaskRay wrote:
> stefanp wrote:
> > MaskRay wrote:
> > > In this case, does the codegen assume that r3 is killed and cannot be reused?
> > This is an artificial test case. There is no real reason why `r4` is used instead of `r3` in the test above. Generating a real test would create more code and it would just clutter the test file. This is a snippet from a real test:
> > ```
> > 10: 00 00 10 04 00 00 60 e4      	pld 3, 0(0), 1
> > 		0000000000000010:  R_PPC64_GOT_TPREL_PCREL34	TGlobal
> > 18: 14 6a c3 7f  	add 30, 3, 13
> > 		0000000000000019:  R_PPC64_TLS	TGlobal
> > 1c: 78 f3 c3 7f  	mr	3, 30
> > 20: 01 00 00 48  	bl 0x20
> > 		0000000000000020:  R_PPC64_REL24_NOTOC	getConst
> > 24: 78 f3 c4 7f  	mr	4, 30
> > ```
> > the idea is that the `bl` clobbers `r3` and so we save to `r30` first so that we can use the result of the add both before and after the call.
> > The only thing I want to test is what happens if the result register of the `add` is different from the result register of the `pld`.
> ```
> pld 3, 12488(0), 1
> add 4, 3, 13
> ```
> 
> r3 != r4. If the compiler generated code makes use of r3, no matter how the linker relaxes the sequence, it will be broken, right?
Is it possible for `r3` to be used for anything other than materializing the address of `x`? Basically, the result in `r3` before the relaxation is "The offset of `x` from the thread pointer" and the result in `r4` is "The address of `x`". After the relaxation, both `r3` and `r4` contain "the address of `x`".


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  https://reviews.llvm.org/D95262/new/

https://reviews.llvm.org/D95262