[AMDGPU][GlobalISel] Remove redundant cmp when copying constant to vcc

[foad]

llvm/lib/Target/AMDGPU/AMDGPUInstructionSelector.cpp

145

Is it really correct to use -1 here if the condition is true? Shouldn't it be "s_mov dst, exec(_lo)" instead?

[arsenm]

llvm/lib/Target/AMDGPU/AMDGPUInstructionSelector.cpp

145

I think it's an open question if an s1 value means a boolean anded with the correct exec mask. My current thinking is the answer is no and the uses that care are responsible for masking out exec bits

llvm/lib/Target/AMDGPU/AMDGPUInstructionSelector.cpp

if (isVCC(DstReg, *MRI)) {
     if (!isVCC(SrcReg, *MRI)) {
       // TODO: Should probably leave the copy and let copyPhysReg expand it.
       if (!RBI.constrainGenericRegister(DstReg, *TRI.getBoolRC(), *MRI))
         return false;
 
       const TargetRegisterClass *SrcRC
         = TRI.getConstrainedRegClassForOperand(Src, *MRI);
 
+      Optional<ValueAndVReg> ConstVal =
+          getConstantVRegValWithLookThrough(SrcReg, *MRI, true, true);
+      if (ConstVal) {
+        unsigned MovOpc =
+            STI.isWave64() ? AMDGPU::S_MOV_B64 : AMDGPU::S_MOV_B32;
+        BuildMI(*BB, &I, DL, TII.get(MovOpc), DstReg)
+            .addImm(ConstVal->Value.getBoolValue() ? -1 : 0);
+      } else {
         Register MaskedReg = MRI->createVirtualRegister(SrcRC);
 
         // We can't trust the high bits at this point, so clear them.
 
         // TODO: Skip masking high bits if def is known boolean.
 
         unsigned AndOpc = TRI.isSGPRClass(SrcRC) ?
           AMDGPU::S_AND_B32 : AMDGPU::V_AND_B32_e32;
         BuildMI(*BB, &I, DL, TII.get(AndOpc), MaskedReg)
             .addImm(1)
             .addReg(SrcReg);
         BuildMI(*BB, &I, DL, TII.get(AMDGPU::V_CMP_NE_U32_e64), DstReg)
             .addImm(0)
             .addReg(MaskedReg);
+      }
 
       if (!MRI->getRegClassOrNull(SrcReg))
         MRI->setRegClass(SrcReg, SrcRC);
       I.eraseFromParent();
       return true;
     }
 
     const TargetRegisterClass *RC =

llvm/test/CodeGen/AMDGPU/GlobalISel/divergent-control-flow.ll

 ; CHECK-NEXT:    s_and_b64 s[2:3], exec, s[2:3]
 ; CHECK-NEXT:    s_or_b64 s[0:1], s[2:3], s[0:1]
 ; CHECK-NEXT:    s_andn2_b64 exec, exec, s[0:1]
 ; CHECK-NEXT:    s_cbranch_execz BB5_4
 ; CHECK-NEXT:  BB5_2: ; %bb1
 ; CHECK-NEXT:    ; =>This Inner Loop Header: Depth=1
 ; CHECK-NEXT:    v_add_u32_e32 v1, 1, v1
 ; CHECK-NEXT:    v_cmp_le_i32_e32 vcc, 0, v1
-; CHECK-NEXT:    v_cmp_ne_u32_e64 s[2:3], 0, 1
+; CHECK-NEXT:    s_mov_b64 s[2:3], -1
 ; CHECK-NEXT:    s_cbranch_vccnz BB5_1
 ; CHECK-NEXT:  ; %bb.3: ; %bb4
 ; CHECK-NEXT:    ; in Loop: Header=BB5_2 Depth=1
 ; CHECK-NEXT:    global_load_dword v2, v[0:1], off glc
 ; CHECK-NEXT:    s_waitcnt vmcnt(0)
 ; CHECK-NEXT:    v_cmp_ge_i32_e64 s[2:3], v0, v2
 ; CHECK-NEXT:    s_branch BB5_1
 ; CHECK-NEXT:  BB5_4: ; %bb9

llvm/test/CodeGen/AMDGPU/GlobalISel/inst-select-copy.mir

bb.0:
     ; WAVE64: S_ENDPGM 0, implicit [[COPY]]
     ; WAVE32-LABEL: name: copy_vcc_lo_to_s32
     ; WAVE32: [[COPY:%[0-9]+]]:sreg_32 = COPY $vcc_lo
     ; WAVE32: S_ENDPGM 0, implicit [[COPY]]
     %0:sgpr(s32) = COPY $vcc_lo
     S_ENDPGM 0, implicit %0
 
 ...
+
+---
+
+name:            copy_s1_to_vcc
+legalized:       true
+regBankSelected: true
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    liveins: $sgpr0_sgpr1
+
+    ; WAVE64-LABEL: name: copy_s1_to_vcc
+    ; WAVE64: liveins: $sgpr0_sgpr1
+    ; WAVE64: [[COPY:%[0-9]+]]:sreg_64 = COPY $sgpr0_sgpr1
+    ; WAVE64: [[COPY1:%[0-9]+]]:sreg_32 = COPY [[COPY]].sub0
+    ; WAVE64: [[S_AND_B32_:%[0-9]+]]:sreg_32 = S_AND_B32 1, [[COPY1]], implicit-def $scc
+    ; WAVE64: [[V_CMP_NE_U32_e64_:%[0-9]+]]:sreg_64 = V_CMP_NE_U32_e64 0, [[S_AND_B32_]], implicit $exec
+    ; WAVE64: S_ENDPGM 0, implicit [[V_CMP_NE_U32_e64_]]
+    ; WAVE32-LABEL: name: copy_s1_to_vcc
+    ; WAVE32: liveins: $sgpr0_sgpr1
+    ; WAVE32: [[COPY:%[0-9]+]]:sreg_64 = COPY $sgpr0_sgpr1
+    ; WAVE32: [[COPY1:%[0-9]+]]:sreg_32 = COPY [[COPY]].sub0
+    ; WAVE32: [[S_AND_B32_:%[0-9]+]]:sreg_32 = S_AND_B32 1, [[COPY1]], implicit-def $scc
+    ; WAVE32: [[V_CMP_NE_U32_e64_:%[0-9]+]]:sreg_32 = V_CMP_NE_U32_e64 0, [[S_AND_B32_]], implicit $exec
+    ; WAVE32: S_ENDPGM 0, implicit [[V_CMP_NE_U32_e64_]]
+    %0:sgpr(s64) = COPY $sgpr0_sgpr1
+    %1:sgpr(s1) = G_TRUNC %0(s64)
+    %2:vcc(s1) = COPY %1(s1)
+    S_ENDPGM 0, implicit %2
+
+...
+
+---
+
+name:            copy_s1_false_to_vcc
+legalized:       true
+regBankSelected: true
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    liveins: $sgpr0
+
+    ; WAVE64-LABEL: name: copy_s1_false_to_vcc
+    ; WAVE64: liveins: $sgpr0
+    ; WAVE64: [[S_MOV_B64_:%[0-9]+]]:sreg_64 = S_MOV_B64 0
+    ; WAVE64: S_ENDPGM 0, implicit [[S_MOV_B64_]]
+    ; WAVE32-LABEL: name: copy_s1_false_to_vcc
+    ; WAVE32: liveins: $sgpr0
+    ; WAVE32: [[S_MOV_B32_:%[0-9]+]]:sreg_32 = S_MOV_B32 0
+    ; WAVE32: S_ENDPGM 0, implicit [[S_MOV_B32_]]
+    %0:sgpr(s1) = G_CONSTANT i1 false
+    %1:vcc(s1) = COPY %0(s1)
+    S_ENDPGM 0, implicit %1
+
+...
+
+---
+
+name:            copy_s1_true_to_vcc
+legalized:       true
+regBankSelected: true
+tracksRegLiveness: true
+body:             |
+  bb.0:
+    liveins: $sgpr0
+
+    ; WAVE64-LABEL: name: copy_s1_true_to_vcc
+    ; WAVE64: liveins: $sgpr0
+    ; WAVE64: [[S_MOV_B64_:%[0-9]+]]:sreg_64 = S_MOV_B64 -1
+    ; WAVE64: S_ENDPGM 0, implicit [[S_MOV_B64_]]
+    ; WAVE32-LABEL: name: copy_s1_true_to_vcc
+    ; WAVE32: liveins: $sgpr0
+    ; WAVE32: [[S_MOV_B32_:%[0-9]+]]:sreg_32 = S_MOV_B32 -1
+    ; WAVE32: S_ENDPGM 0, implicit [[S_MOV_B32_]]
+    %0:sgpr(s1) = G_CONSTANT i1 true
+    %1:vcc(s1) = COPY %0(s1)
+    S_ENDPGM 0, implicit %1
+
+...

llvm/test/CodeGen/AMDGPU/GlobalISel/llvm.amdgcn.div.fmas.ll

 
 define amdgpu_kernel void @test_div_fmas_f32_imm_false_cond_to_vcc(float addrspace(1)* %out, [8 x i32], float %a, [8 x i32], float %b, [8 x i32], float %c) {
 ; GFX7-LABEL: test_div_fmas_f32_imm_false_cond_to_vcc:
 ; GFX7:       ; %bb.0:
 ; GFX7-NEXT:    s_load_dwordx2 s[4:5], s[0:1], 0x9
 ; GFX7-NEXT:    s_load_dword s2, s[0:1], 0x13
 ; GFX7-NEXT:    s_load_dword s3, s[0:1], 0x1c
 ; GFX7-NEXT:    s_load_dword s0, s[0:1], 0x25
-; GFX7-NEXT:    v_cmp_ne_u32_e64 vcc, 0, 0
+; GFX7-NEXT:    s_mov_b64 vcc, 0
 ; GFX7-NEXT:    s_mov_b32 s6, -1
 ; GFX7-NEXT:    s_waitcnt lgkmcnt(0)
 ; GFX7-NEXT:    v_mov_b32_e32 v0, s2
 ; GFX7-NEXT:    v_mov_b32_e32 v1, s3
 ; GFX7-NEXT:    v_mov_b32_e32 v2, s0
 ; GFX7-NEXT:    v_div_fmas_f32 v0, v0, v1, v2
 ; GFX7-NEXT:    s_mov_b32 s7, 0xf000
 ; GFX7-NEXT:    buffer_store_dword v0, off, s[4:7], 0
 ; GFX7-NEXT:    s_endpgm
 ;
 ; GFX8-LABEL: test_div_fmas_f32_imm_false_cond_to_vcc:
 ; GFX8:       ; %bb.0:
 ; GFX8-NEXT:    s_load_dword s2, s[0:1], 0x4c
 ; GFX8-NEXT:    s_load_dword s3, s[0:1], 0x70
 ; GFX8-NEXT:    s_load_dword s4, s[0:1], 0x94
-; GFX8-NEXT:    v_cmp_ne_u32_e64 vcc, 0, 0
+; GFX8-NEXT:    s_mov_b64 vcc, 0
 ; GFX8-NEXT:    s_load_dwordx2 s[0:1], s[0:1], 0x24
 ; GFX8-NEXT:    s_waitcnt lgkmcnt(0)
 ; GFX8-NEXT:    v_mov_b32_e32 v0, s2
 ; GFX8-NEXT:    v_mov_b32_e32 v1, s3
 ; GFX8-NEXT:    v_mov_b32_e32 v2, s4
 ; GFX8-NEXT:    v_div_fmas_f32 v2, v0, v1, v2
 ; GFX8-NEXT:    v_mov_b32_e32 v0, s0
 ; GFX8-NEXT:    v_mov_b32_e32 v1, s1
 ; GFX8-NEXT:    flat_store_dword v[0:1], v2
 ; GFX8-NEXT:    s_endpgm
 ;
 ; GFX10_W32-LABEL: test_div_fmas_f32_imm_false_cond_to_vcc:
 ; GFX10_W32:       ; %bb.0:
 ; GFX10_W32-NEXT:    s_clause 0x3
 ; GFX10_W32-NEXT:    s_load_dword s5, s[0:1], 0x70
 ; GFX10_W32-NEXT:    s_load_dword s6, s[0:1], 0x94
 ; GFX10_W32-NEXT:    s_load_dword s4, s[0:1], 0x4c
 ; GFX10_W32-NEXT:    s_load_dwordx2 s[2:3], s[0:1], 0x24
-; GFX10_W32-NEXT:    v_cmp_ne_u32_e64 vcc_lo, 0, 0
+; GFX10_W32-NEXT:    s_mov_b32 vcc_lo, 0
 ; GFX10_W32-NEXT:    s_waitcnt lgkmcnt(0)
 ; GFX10_W32-NEXT:    v_mov_b32_e32 v0, s5
 ; GFX10_W32-NEXT:    v_mov_b32_e32 v1, s6
 ; GFX10_W32-NEXT:    v_div_fmas_f32 v0, s4, v0, v1
 ; GFX10_W32-NEXT:    v_mov_b32_e32 v1, 0
 ; GFX10_W32-NEXT:    global_store_dword v1, v0, s[2:3]
 ; GFX10_W32-NEXT:    s_endpgm
 ;
 ; GFX10_W64-LABEL: test_div_fmas_f32_imm_false_cond_to_vcc:
 ; GFX10_W64:       ; %bb.0:
 ; GFX10_W64-NEXT:    s_clause 0x3
 ; GFX10_W64-NEXT:    s_load_dword s5, s[0:1], 0x70
 ; GFX10_W64-NEXT:    s_load_dword s6, s[0:1], 0x94
 ; GFX10_W64-NEXT:    s_load_dword s4, s[0:1], 0x4c
 ; GFX10_W64-NEXT:    s_load_dwordx2 s[2:3], s[0:1], 0x24
-; GFX10_W64-NEXT:    v_cmp_ne_u32_e64 vcc, 0, 0
+; GFX10_W64-NEXT:    s_mov_b64 vcc, 0
 ; GFX10_W64-NEXT:    s_waitcnt lgkmcnt(0)
 ; GFX10_W64-NEXT:    v_mov_b32_e32 v0, s5
 ; GFX10_W64-NEXT:    v_mov_b32_e32 v1, s6
 ; GFX10_W64-NEXT:    v_div_fmas_f32 v0, s4, v0, v1
 ; GFX10_W64-NEXT:    v_mov_b32_e32 v1, 0
 ; GFX10_W64-NEXT:    global_store_dword v1, v0, s[2:3]
 ; GFX10_W64-NEXT:    s_endpgm
   %result = call float @llvm.amdgcn.div.fmas.f32(float %a, float %b, float %c, i1 false)
   store float %result, float addrspace(1)* %out, align 4
   ret void
 }
 
 define amdgpu_kernel void @test_div_fmas_f32_imm_true_cond_to_vcc(float addrspace(1)* %out, [8 x i32], float %a, [8 x i32], float %b, [8 x i32], float %c) {
 ; GFX7-LABEL: test_div_fmas_f32_imm_true_cond_to_vcc:
 ; GFX7:       ; %bb.0:
 ; GFX7-NEXT:    s_load_dwordx2 s[4:5], s[0:1], 0x9
 ; GFX7-NEXT:    s_load_dword s2, s[0:1], 0x13
 ; GFX7-NEXT:    s_load_dword s3, s[0:1], 0x1c
 ; GFX7-NEXT:    s_load_dword s0, s[0:1], 0x25
-; GFX7-NEXT:    v_cmp_ne_u32_e64 vcc, 0, 1
+; GFX7-NEXT:    s_mov_b64 vcc, -1
 ; GFX7-NEXT:    s_mov_b32 s6, -1
 ; GFX7-NEXT:    s_waitcnt lgkmcnt(0)
 ; GFX7-NEXT:    v_mov_b32_e32 v0, s2
 ; GFX7-NEXT:    v_mov_b32_e32 v1, s3
 ; GFX7-NEXT:    v_mov_b32_e32 v2, s0
 ; GFX7-NEXT:    v_div_fmas_f32 v0, v0, v1, v2
 ; GFX7-NEXT:    s_mov_b32 s7, 0xf000
 ; GFX7-NEXT:    buffer_store_dword v0, off, s[4:7], 0
 ; GFX7-NEXT:    s_endpgm
 ;
 ; GFX8-LABEL: test_div_fmas_f32_imm_true_cond_to_vcc:
 ; GFX8:       ; %bb.0:
 ; GFX8-NEXT:    s_load_dword s2, s[0:1], 0x4c
 ; GFX8-NEXT:    s_load_dword s3, s[0:1], 0x70
 ; GFX8-NEXT:    s_load_dword s4, s[0:1], 0x94
-; GFX8-NEXT:    v_cmp_ne_u32_e64 vcc, 0, 1
+; GFX8-NEXT:    s_mov_b64 vcc, -1
 ; GFX8-NEXT:    s_load_dwordx2 s[0:1], s[0:1], 0x24
 ; GFX8-NEXT:    s_waitcnt lgkmcnt(0)
 ; GFX8-NEXT:    v_mov_b32_e32 v0, s2
 ; GFX8-NEXT:    v_mov_b32_e32 v1, s3
 ; GFX8-NEXT:    v_mov_b32_e32 v2, s4
 ; GFX8-NEXT:    v_div_fmas_f32 v2, v0, v1, v2
 ; GFX8-NEXT:    v_mov_b32_e32 v0, s0
 ; GFX8-NEXT:    v_mov_b32_e32 v1, s1
 ; GFX8-NEXT:    flat_store_dword v[0:1], v2
 ; GFX8-NEXT:    s_endpgm
 ;
 ; GFX10_W32-LABEL: test_div_fmas_f32_imm_true_cond_to_vcc:
 ; GFX10_W32:       ; %bb.0:
 ; GFX10_W32-NEXT:    s_clause 0x3
 ; GFX10_W32-NEXT:    s_load_dword s5, s[0:1], 0x70
 ; GFX10_W32-NEXT:    s_load_dword s6, s[0:1], 0x94
 ; GFX10_W32-NEXT:    s_load_dword s4, s[0:1], 0x4c
 ; GFX10_W32-NEXT:    s_load_dwordx2 s[2:3], s[0:1], 0x24
-; GFX10_W32-NEXT:    v_cmp_ne_u32_e64 vcc_lo, 0, 1
+; GFX10_W32-NEXT:    s_mov_b32 vcc_lo, -1
 ; GFX10_W32-NEXT:    s_waitcnt lgkmcnt(0)
 ; GFX10_W32-NEXT:    v_mov_b32_e32 v0, s5
 ; GFX10_W32-NEXT:    v_mov_b32_e32 v1, s6
 ; GFX10_W32-NEXT:    v_div_fmas_f32 v0, s4, v0, v1
 ; GFX10_W32-NEXT:    v_mov_b32_e32 v1, 0
 ; GFX10_W32-NEXT:    global_store_dword v1, v0, s[2:3]
 ; GFX10_W32-NEXT:    s_endpgm
 ;
 ; GFX10_W64-LABEL: test_div_fmas_f32_imm_true_cond_to_vcc:
 ; GFX10_W64:       ; %bb.0:
 ; GFX10_W64-NEXT:    s_clause 0x3
 ; GFX10_W64-NEXT:    s_load_dword s5, s[0:1], 0x70
 ; GFX10_W64-NEXT:    s_load_dword s6, s[0:1], 0x94
 ; GFX10_W64-NEXT:    s_load_dword s4, s[0:1], 0x4c
 ; GFX10_W64-NEXT:    s_load_dwordx2 s[2:3], s[0:1], 0x24
-; GFX10_W64-NEXT:    v_cmp_ne_u32_e64 vcc, 0, 1
+; GFX10_W64-NEXT:    s_mov_b64 vcc, -1
 ; GFX10_W64-NEXT:    s_waitcnt lgkmcnt(0)
 ; GFX10_W64-NEXT:    v_mov_b32_e32 v0, s5
 ; GFX10_W64-NEXT:    v_mov_b32_e32 v1, s6
 ; GFX10_W64-NEXT:    v_div_fmas_f32 v0, s4, v0, v1
 ; GFX10_W64-NEXT:    v_mov_b32_e32 v1, 0
 ; GFX10_W64-NEXT:    global_store_dword v1, v0, s[2:3]
 ; GFX10_W64-NEXT:    s_endpgm
   %result = call float @llvm.amdgcn.div.fmas.f32(float %a, float %b, float %c, i1 true)

llvm/test/CodeGen/AMDGPU/GlobalISel/localizer.ll

 @static.gv3 = internal addrspace(1) global i32 undef, align 4
 
 define void @localize_internal_globals(i1 %cond) {
 ; GFX9-LABEL: localize_internal_globals:
 ; GFX9:       ; %bb.0: ; %entry
 ; GFX9-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
 ; GFX9-NEXT:    v_and_b32_e32 v0, 1, v0
 ; GFX9-NEXT:    v_cmp_ne_u32_e32 vcc, 0, v0
-; GFX9-NEXT:    v_cmp_ne_u32_e64 s[4:5], 0, 1
-; GFX9-NEXT:    s_xor_b64 s[4:5], vcc, s[4:5]
+; GFX9-NEXT:    s_xor_b64 s[4:5], vcc, -1
 ; GFX9-NEXT:    s_and_saveexec_b64 s[6:7], s[4:5]
 ; GFX9-NEXT:    s_xor_b64 s[4:5], exec, s[6:7]
 ; GFX9-NEXT:    s_cbranch_execz BB2_2
 ; GFX9-NEXT:  ; %bb.1: ; %bb1
 ; GFX9-NEXT:    s_getpc_b64 s[6:7]
 ; GFX9-NEXT:    s_add_u32 s6, s6, static.gv2@rel32@lo+4
 ; GFX9-NEXT:    s_addc_u32 s7, s7, static.gv2@rel32@hi+12
 ; GFX9-NEXT:    v_mov_b32_e32 v0, 0