[llvm] [AMDGPU] Fix getDestEquivalentVGPRClass narrowing AV-class registers (PR #212963)

[via llvm-commits]

llvmorg-github-actions[bot] wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-backend-amdgpu

Author: Arseniy Obolenskiy (aobolensk)

<details>
<summary>Changes</summary>

isVGPRClass() rejects AV-class registers, so they were narrowed to VGPR-only instead of preserved. Same reasoning behind the fix as in SIPreAllocateWWMRegs (see https://github.com/llvm/llvm-project/pull/211560)

---
Full diff: https://github.com/llvm/llvm-project/pull/212963.diff


2 Files Affected:

- (modified) llvm/lib/Target/AMDGPU/SIInstrInfo.cpp (+1-1) 
- (modified) llvm/test/CodeGen/AMDGPU/si-fix-sgpr-copies-av-constrain.mir (+19) 


``````````diff
diff --git a/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp b/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp
index d3a5c1e1cf281..ee5db6c45fa52 100644
--- a/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp
+++ b/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp
@@ -9808,7 +9808,7 @@ const TargetRegisterClass *SIInstrInfo::getDestEquivalentVGPRClass(
       if (!NewDstRC)
         return nullptr;
     } else {
-      if (RI.isVGPRClass(NewDstRC) || NewDstRC == &AMDGPU::VReg_1RegClass)
+      if (RI.hasVGPRs(NewDstRC) || NewDstRC == &AMDGPU::VReg_1RegClass)
         return nullptr;
 
       NewDstRC = RI.getEquivalentVGPRClass(NewDstRC);
diff --git a/llvm/test/CodeGen/AMDGPU/si-fix-sgpr-copies-av-constrain.mir b/llvm/test/CodeGen/AMDGPU/si-fix-sgpr-copies-av-constrain.mir
index f8a22f20c57d6..7f208b1659acf 100644
--- a/llvm/test/CodeGen/AMDGPU/si-fix-sgpr-copies-av-constrain.mir
+++ b/llvm/test/CodeGen/AMDGPU/si-fix-sgpr-copies-av-constrain.mir
@@ -109,3 +109,22 @@ body:             |
     $m0 = COPY %1.sub0
 ...
 
+# The V2S copy has no SALU-only use chain, so it is turned to VALU via
+# moveToVALU instead of v_readfirstlane_b32. getDestEquivalentVGPRClass
+# must not narrow the AV-class source to a VGPR-only class.
+---
+name:            moveto_valu_preserves_av
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    liveins: $vgpr0_vgpr1_vgpr2_vgpr3_vgpr4_vgpr5_vgpr6_vgpr7_vgpr8_vgpr9_vgpr10_vgpr11_vgpr12_vgpr13_vgpr14_vgpr15
+
+    ; CHECK-LABEL: name: moveto_valu_preserves_av
+    ; CHECK: liveins: $vgpr0_vgpr1_vgpr2_vgpr3_vgpr4_vgpr5_vgpr6_vgpr7_vgpr8_vgpr9_vgpr10_vgpr11_vgpr12_vgpr13_vgpr14_vgpr15
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: [[COPY:%[0-9]+]]:vreg_512_align2 = COPY $vgpr0_vgpr1_vgpr2_vgpr3_vgpr4_vgpr5_vgpr6_vgpr7_vgpr8_vgpr9_vgpr10_vgpr11_vgpr12_vgpr13_vgpr14_vgpr15
+    ; CHECK-NEXT: S_NOP 0, implicit [[COPY]]
+    %0:av_512 = COPY $vgpr0_vgpr1_vgpr2_vgpr3_vgpr4_vgpr5_vgpr6_vgpr7_vgpr8_vgpr9_vgpr10_vgpr11_vgpr12_vgpr13_vgpr14_vgpr15
+    %1:sgpr_512 = COPY %0
+    S_NOP 0, implicit %1
+...

``````````

</details>


https://github.com/llvm/llvm-project/pull/212963