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Summary: Somehow, I first interpreted the docs as saying space for xnack_mask is only reserved when XNACK is enabled via SH_MEM_CONFIG. I felt uneasy about this and went back to actually test what is happening, and it turns out that xnack_mask is always reserved at least on Tonga and Carrizo, in the sense that flat_scr is always fixed below the SGPRs that are used to implement xnack_mask, whether or not they are actually used. I confirmed this by writing a shader using inline assembly to tease out the aliasing between flat_scratch and regular SGPRs. For example, on Tonga, where we fix the number of SGPRs to 80, s[74:75] aliases flat_scratch (so xnack_mask is s[76:77] and vcc is s[78:79]). This patch changes both the calculation of the total number of SGPRs and the various register reservations to account for this. It ought to be possible to use the gap left by xnack_mask when the feature isn't used, but this patch doesn't try to do that. (Note that the same applies to vcc.) Note that previously, even before my earlier change in r256794, the SGPRs that alias to xnack_mask could end up being used as well when flat_scr was unused and the total number of SGPRs happened to fall on the right alignment (e.g. highest regular SGPR being used s29 and VCC used would lead to number of SGPRs being 32, where s28 and s29 alias with xnack_mask). So if there were some conflict due to such aliasing, we should have noticed that already. Reviewers: arsenm, tstellarAMD Subscribers: arsenm, llvm-commits Differential Revision: http://reviews.llvm.org/D15898 llvm-svn: 257073
40 lines
1.1 KiB
LLVM
40 lines
1.1 KiB
LLVM
; RUN: llc < %s -march=amdgcn -mcpu=kaveri -verify-machineinstrs | FileCheck %s --check-prefix=GCN --check-prefix=CI --check-prefix=NO-XNACK
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; RUN: llc < %s -march=amdgcn -mcpu=fiji -verify-machineinstrs | FileCheck %s --check-prefix=GCN --check-prefix=VI --check-prefix=NO-XNACK
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; RUN: llc < %s -march=amdgcn -mcpu=carrizo -mattr=+xnack -verify-machineinstrs | FileCheck %s --check-prefix=GCN --check-prefix=VI --check-prefix=XNACK
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; GCN-LABEL: {{^}}no_vcc_no_flat:
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; NO-XNACK: ; NumSgprs: 8
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; XNACK: ; NumSgprs: 12
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define void @no_vcc_no_flat() {
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entry:
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call void asm sideeffect "", "~{SGPR7}"()
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ret void
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}
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; GCN-LABEL: {{^}}vcc_no_flat:
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; NO-XNACK: ; NumSgprs: 10
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; XNACK: ; NumSgprs: 12
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define void @vcc_no_flat() {
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entry:
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call void asm sideeffect "", "~{SGPR7},~{VCC}"()
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ret void
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}
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; GCN-LABEL: {{^}}no_vcc_flat:
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; CI: ; NumSgprs: 12
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; VI: ; NumSgprs: 14
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define void @no_vcc_flat() {
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entry:
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call void asm sideeffect "", "~{SGPR7},~{FLAT_SCR}"()
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ret void
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}
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; GCN-LABEL: {{^}}vcc_flat:
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; CI: ; NumSgprs: 12
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; VI: ; NumSgprs: 14
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define void @vcc_flat() {
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entry:
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call void asm sideeffect "", "~{SGPR7},~{VCC},~{FLAT_SCR}"()
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ret void
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}
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