[llvm] AMDGPU: Mark scc clobbers in the simulated trap expansion dead (PR #227633)

[Matt Arsenault via llvm-commits]

https://github.com/arsenm updated https://github.com/llvm/llvm-project/pull/227633

>From 31db0f0d1d99953ae25c80b1819e6be1636f3ea5 Mon Sep 17 00:00:00 2001
From: Matt Arsenault <Matthew.Arsenault at amd.com>
Date: Tue, 29 Sep 2026 03:33:49 +0200
Subject: [PATCH] AMDGPU: Mark scc clobbers in the simulated trap expansion
 dead

Co-Authored-By: Claude Opus 5 <noreply at anthropic.com>
---
 llvm/lib/Target/AMDGPU/SIInstrInfo.cpp                    | 6 ++++--
 .../CodeGen/AMDGPU/GlobalISel/legalize-trap-gfx11.mir     | 8 ++++----
 2 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp b/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp
index 1d1f26a5e9210..743ced76a122f 100644
--- a/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp
+++ b/llvm/lib/Target/AMDGPU/SIInstrInfo.cpp
@@ -2073,12 +2073,14 @@ MachineBasicBlock *SIInstrInfo::insertSimulatedTrap(MachineRegisterInfo &MRI,
       MRI.createVirtualRegister(&AMDGPU::SReg_32RegClass);
   BuildMI(*TrapBB, TrapBB->end(), DL, get(AMDGPU::S_AND_B32), DoorbellRegMasked)
       .addUse(DoorbellReg)
-      .addImm(DoorbellIDMask);
+      .addImm(DoorbellIDMask)
+      .setOperandDead(3); // implicit-def $scc
   Register SetWaveAbortBit =
       MRI.createVirtualRegister(&AMDGPU::SReg_32RegClass);
   BuildMI(*TrapBB, TrapBB->end(), DL, get(AMDGPU::S_OR_B32), SetWaveAbortBit)
       .addUse(DoorbellRegMasked)
-      .addImm(ECQueueWaveAbort);
+      .addImm(ECQueueWaveAbort)
+      .setOperandDead(3); // implicit-def $scc
   BuildMI(*TrapBB, TrapBB->end(), DL, get(AMDGPU::S_MOV_B32), AMDGPU::M0)
       .addUse(SetWaveAbortBit);
   BuildMI(*TrapBB, TrapBB->end(), DL, get(AMDGPU::S_SENDMSG))
diff --git a/llvm/test/CodeGen/AMDGPU/GlobalISel/legalize-trap-gfx11.mir b/llvm/test/CodeGen/AMDGPU/GlobalISel/legalize-trap-gfx11.mir
index b35b2343036a4..aa86f17579429 100644
--- a/llvm/test/CodeGen/AMDGPU/GlobalISel/legalize-trap-gfx11.mir
+++ b/llvm/test/CodeGen/AMDGPU/GlobalISel/legalize-trap-gfx11.mir
@@ -26,8 +26,8 @@ body: |
     ; GFX1100-NEXT: S_TRAP 2
     ; GFX1100-NEXT: [[S_SENDMSG_RTN_B32_:%[0-9]+]]:sreg_32 = S_SENDMSG_RTN_B32 128
     ; GFX1100-NEXT: $ttmp2 = S_MOV_B32 $m0
-    ; GFX1100-NEXT: [[S_AND_B32_:%[0-9]+]]:sreg_32 = S_AND_B32 [[S_SENDMSG_RTN_B32_]], 1023, implicit-def $scc
-    ; GFX1100-NEXT: [[S_OR_B32_:%[0-9]+]]:sreg_32 = S_OR_B32 [[S_AND_B32_]], 1024, implicit-def $scc
+    ; GFX1100-NEXT: [[S_AND_B32_:%[0-9]+]]:sreg_32 = S_AND_B32 [[S_SENDMSG_RTN_B32_]], 1023, implicit-def dead $scc
+    ; GFX1100-NEXT: [[S_OR_B32_:%[0-9]+]]:sreg_32 = S_OR_B32 [[S_AND_B32_]], 1024, implicit-def dead $scc
     ; GFX1100-NEXT: $m0 = S_MOV_B32 [[S_OR_B32_]]
     ; GFX1100-NEXT: S_SENDMSG 1, implicit $exec, implicit $m0
     ; GFX1100-NEXT: $m0 = S_MOV_B32 $ttmp2
@@ -75,8 +75,8 @@ body: |
   ; GFX1100-NEXT:   S_TRAP 2
   ; GFX1100-NEXT:   [[S_SENDMSG_RTN_B32_:%[0-9]+]]:sreg_32 = S_SENDMSG_RTN_B32 128
   ; GFX1100-NEXT:   $ttmp2 = S_MOV_B32 $m0
-  ; GFX1100-NEXT:   [[S_AND_B32_:%[0-9]+]]:sreg_32 = S_AND_B32 [[S_SENDMSG_RTN_B32_]], 1023, implicit-def $scc
-  ; GFX1100-NEXT:   [[S_OR_B32_:%[0-9]+]]:sreg_32 = S_OR_B32 [[S_AND_B32_]], 1024, implicit-def $scc
+  ; GFX1100-NEXT:   [[S_AND_B32_:%[0-9]+]]:sreg_32 = S_AND_B32 [[S_SENDMSG_RTN_B32_]], 1023, implicit-def dead $scc
+  ; GFX1100-NEXT:   [[S_OR_B32_:%[0-9]+]]:sreg_32 = S_OR_B32 [[S_AND_B32_]], 1024, implicit-def dead $scc
   ; GFX1100-NEXT:   $m0 = S_MOV_B32 [[S_OR_B32_]]
   ; GFX1100-NEXT:   S_SENDMSG 1, implicit $exec, implicit $m0
   ; GFX1100-NEXT:   $m0 = S_MOV_B32 $ttmp2