AMDGPU: Use an ABS32_LO relocation for SCRATCH_RSRC_DWORD1

[nhaehnle]

Summary

Using HI here makes no logical sense, since the dword is only
32 bits to begin with.

Current Mesa master does not look at the relocation type at all,
so this change is fine. Future Mesa will rely on this, however.

Change-Id: I91085707834c4ac0370926602b93c94b90e44cb1

[arsenm]

I thought mesa was moving to stop using the relocations at all for this?

[nhaehnle]

In D55369#1321530, @arsenm wrote:

I thought mesa was moving to stop using the relocations at all for this?

Eventually I hope so, yes.

[arsenm]

LGTM

llvm/trunk/lib/Target/AMDGPU/MCTargetDesc/AMDGPUELFObjectWriter.cpp

 
 unsigned AMDGPUELFObjectWriter::getRelocType(MCContext &Ctx,
                                              const MCValue &Target,
                                              const MCFixup &Fixup,
                                              bool IsPCRel) const {
   if (const auto *SymA = Target.getSymA()) {
     // SCRATCH_RSRC_DWORD[01] is a special global variable that represents
     // the scratch buffer.
-    if (SymA->getSymbol().getName() == "SCRATCH_RSRC_DWORD0")
+    if (SymA->getSymbol().getName() == "SCRATCH_RSRC_DWORD0" ||
+        SymA->getSymbol().getName() == "SCRATCH_RSRC_DWORD1")
       return ELF::R_AMDGPU_ABS32_LO;
-
-    if (SymA->getSymbol().getName() == "SCRATCH_RSRC_DWORD1")
-      return ELF::R_AMDGPU_ABS32_HI;
   }
 
   switch (Target.getAccessVariant()) {
   default:
     break;
   case MCSymbolRefExpr::VK_GOTPCREL:
     return ELF::R_AMDGPU_GOTPCREL;
   case MCSymbolRefExpr::VK_AMDGPU_GOTPCREL32_LO:

llvm/trunk/test/CodeGen/AMDGPU/scratch-simple.ll

 ; RUN: llc -march=amdgcn -mtriple=amdgcn-- -mcpu=verde -verify-machineinstrs < %s | FileCheck --check-prefix=GCN --check-prefix=SI %s
 ; RUN: llc -march=amdgcn -mtriple=amdgcn-- -mcpu=gfx803 -mattr=-flat-for-global -verify-machineinstrs < %s | FileCheck --check-prefix=GCN --check-prefix=SI %s
 ; RUN: llc -march=amdgcn -mtriple=amdgcn-- -mcpu=gfx900 -mattr=-flat-for-global -verify-machineinstrs < %s | FileCheck --check-prefix=GCN --check-prefix=GFX9 %s
+; RUN: llc -march=amdgcn -mtriple=amdgcn-- -mcpu=gfx900 -filetype=obj < %s | llvm-readobj -relocations | FileCheck --check-prefix=RELS %s
+
+; RELS: R_AMDGPU_ABS32_LO SCRATCH_RSRC_DWORD0 0x0
+; RELS: R_AMDGPU_ABS32_LO SCRATCH_RSRC_DWORD1 0x0
 
 ; This used to fail due to a v_add_i32 instruction with an illegal immediate
 ; operand that was created during Local Stack Slot Allocation. Test case derived
 ; from https://bugs.freedesktop.org/show_bug.cgi?id=96602
 ;
 ; GCN-LABEL: {{^}}ps_main:
 
 ; GCN-DAG: s_mov_b32 s4, SCRATCH_RSRC_DWORD0