AMDGPU: Preserve undef flag when expanding SI_IF

[arsenm]

Summary

Fixes undefined value verifier error.

[rampitec]

LGTM

[arsenm]

r355426

lib/Target/AMDGPU/SILowerControlFlow.cpp

MachineInstr *CopyExec =
     .addReg(AMDGPU::EXEC)
     .addReg(AMDGPU::EXEC, RegState::ImplicitDefine);
 
   unsigned Tmp = MRI->createVirtualRegister(&AMDGPU::SReg_64RegClass);
 
   MachineInstr *And =
     BuildMI(MBB, I, DL, TII->get(AMDGPU::S_AND_B64), Tmp)
     .addReg(CopyReg)
-    //.addReg(AMDGPU::EXEC)
-    .addReg(Cond.getReg());
+    .add(Cond);
+
   setImpSCCDefDead(*And, true);
 
   MachineInstr *Xor = nullptr;
   if (!SimpleIf) {
     Xor =
       BuildMI(MBB, I, DL, TII->get(AMDGPU::S_XOR_B64), SaveExecReg)
       .addReg(Tmp)
       .addReg(CopyReg);

test/CodeGen/AMDGPU/si-lower-control-flow.mir

+# NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py
 # RUN: llc -mtriple=amdgcn-amd-amdhsa -run-pass=si-lower-control-flow -verify-machineinstrs %s -o - | FileCheck -check-prefixes=GCN %s
 
 # Check that assert is not triggered
-# GCN-LABEL: name: si-lower-control-flow{{$}}
-# GCN-CHECK: S_LOAD_DWORD_IMM
-
---- |
-
-  define amdgpu_kernel void @si-lower-control-flow() {
-    ret void
-  }
 
 ...
 ---
 name: si-lower-control-flow
 body: |
   bb.0:
+    ; GCN-LABEL: name: si-lower-control-flow
+    ; GCN: [[COPY:%[0-9]+]]:sgpr_64 = COPY $sgpr4_sgpr5
+    ; GCN: [[S_LOAD_DWORD_IMM:%[0-9]+]]:sreg_32_xm0_xexec = S_LOAD_DWORD_IMM [[COPY]], 16, 0
+    ; GCN: [[S_AND_B32_:%[0-9]+]]:sreg_32_xm0 = S_AND_B32 [[S_LOAD_DWORD_IMM]], 255, implicit-def $scc
+    ; GCN: [[S_AND_B32_1:%[0-9]+]]:sreg_32_xm0 = S_AND_B32 65535, [[S_AND_B32_]], implicit-def $scc
+    ; GCN: S_ENDPGM
     %0:sgpr_64 = COPY $sgpr4_sgpr5
     %1:sreg_32_xm0_xexec = S_LOAD_DWORD_IMM %0, 16, 0
     %2:sreg_32_xm0 = S_AND_B32 %1, 255, implicit-def $scc
     %3:sreg_32_xm0 = S_AND_B32 65535, %2, implicit-def $scc
     S_ENDPGM
 ...
+
+---
+name: preserve_undef_flag_si_if_src
+tracksRegLiveness: true
+body:             |
+  ; GCN-LABEL: name: preserve_undef_flag_si_if_src
+  ; GCN: bb.0:
+  ; GCN:   successors: %bb.1(0x40000000), %bb.2(0x40000000)
+  ; GCN:   [[COPY:%[0-9]+]]:sreg_64 = COPY $exec, implicit-def $exec
+  ; GCN:   [[S_AND_B64_:%[0-9]+]]:sreg_64 = S_AND_B64 [[COPY]], undef %1:sreg_64, implicit-def dead $scc
+  ; GCN:   [[S_XOR_B64_:%[0-9]+]]:sreg_64 = S_XOR_B64 [[S_AND_B64_]], [[COPY]], implicit-def dead $scc
+  ; GCN:   $exec = S_MOV_B64_term killed [[S_AND_B64_]]
+  ; GCN:   SI_MASK_BRANCH %bb.2, implicit $exec
+  ; GCN:   S_BRANCH %bb.1
+  ; GCN: bb.1:
+  ; GCN:   successors: %bb.2(0x80000000)
+  ; GCN: bb.2:
+  ; GCN:   S_ENDPGM
+  bb.0:
+    successors: %bb.1, %bb.2
+
+    %1:sreg_64 = SI_IF undef %0:sreg_64, %bb.2, implicit-def dead $exec, implicit-def dead $scc, implicit $exec
+    S_BRANCH %bb.1
+
+  bb.1:
+    successors: %bb.2
+
+  bb.2:
+    S_ENDPGM
+
+...