PeepholeOpt: Handle subregister compose when looking through reg_sequence (llvm#127051)

Previously this would give up on folding subregister copies through
a reg_sequence if the input operand already had a subregister index.
d246cc6 stopped introducing these
subregister uses, and this is the first step to lifting that restriction.

I was expecting to be able to implement this only purely with compose /
reverse compose, but I wasn't able to make it work so relies on testing
the lanemasks for whether the copy reads a subset of the input.

Author: arsenm

llvm/lib/CodeGen/PeepholeOptimizer.cpp

@@ -1984,12 +1984,43 @@ ValueTrackerResult ValueTracker::getNextSourceFromRegSequence() {
 
   // We are looking at:
   // Def = REG_SEQUENCE v0, sub0, v1, sub1, ...
-  // Check if one of the operand defines the subreg we are interested in.
+  //
+  // Check if one of the operands exactly defines the subreg we are interested
+  // in.
   for (const RegSubRegPairAndIdx &RegSeqInput : RegSeqInputRegs) {
     if (RegSeqInput.SubIdx == DefSubReg)
       return ValueTrackerResult(RegSeqInput.Reg, RegSeqInput.SubReg);
   }
 
+  const TargetRegisterInfo *TRI = MRI.getTargetRegisterInfo();
+
+  // If we did not find an exact match, see if we can do a composition to
+  // extract a sub-subregister.
+  for (const RegSubRegPairAndIdx &RegSeqInput : RegSeqInputRegs) {
+    // We don't check if the resulting class supports the subregister index
+    // yet. This will occur before any rewrite when looking for an eligible
+    // source.
+
+    LaneBitmask DefMask = TRI->getSubRegIndexLaneMask(DefSubReg);
+    LaneBitmask ThisOpRegMask = TRI->getSubRegIndexLaneMask(RegSeqInput.SubIdx);
+
+    // Check that this extract reads a subset of this single reg_sequence input.
+    //
+    // FIXME: We should be able to filter this in terms of the indexes directly
+    // without checking the lanemasks.
+    if ((DefMask & ThisOpRegMask) != DefMask)
+      continue;
+
+    unsigned ReverseDefCompose =
+        TRI->reverseComposeSubRegIndices(RegSeqInput.SubIdx, DefSubReg);
+    if (!ReverseDefCompose)
+      continue;
+
+    unsigned ComposedDefInSrcReg1 =
+        TRI->composeSubRegIndices(RegSeqInput.SubReg, ReverseDefCompose);
+    return ValueTrackerResult(RegSeqInput.Reg, ComposedDefInSrcReg1);
+  }
+
   // If the subreg we are tracking is super-defined by another subreg,
   // we could follow this value. However, this would require to compose
   // the subreg and we do not do that for now.

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

@@ -2872,8 +2872,8 @@ define double @dyn_extract_v7f64_v_v(<7 x double> %vec, i32 %sel) {
 ; GCN-NEXT:    v_cndmask_b32_e32 v0, v0, v12, vcc
 ; GCN-NEXT:    v_cndmask_b32_e32 v1, v1, v13, vcc
 ; GCN-NEXT:    v_cmp_eq_u32_e32 vcc, 7, v14
-; GCN-NEXT:    v_cndmask_b32_e32 v0, v0, v14, vcc
-; GCN-NEXT:    v_cndmask_b32_e32 v1, v1, v15, vcc
+; GCN-NEXT:    v_cndmask_b32_e32 v0, v0, v0, vcc
+; GCN-NEXT:    v_cndmask_b32_e32 v1, v1, v1, vcc
 ; GCN-NEXT:    s_setpc_b64 s[30:31]
 ;
 ; GFX10-LABEL: dyn_extract_v7f64_v_v:
@@ -2898,8 +2898,8 @@ define double @dyn_extract_v7f64_v_v(<7 x double> %vec, i32 %sel) {
 ; GFX10-NEXT:    v_cndmask_b32_e32 v0, v0, v12, vcc_lo
 ; GFX10-NEXT:    v_cndmask_b32_e32 v1, v1, v13, vcc_lo
 ; GFX10-NEXT:    v_cmp_eq_u32_e32 vcc_lo, 7, v14
-; GFX10-NEXT:    v_cndmask_b32_e32 v0, v0, v14, vcc_lo
-; GFX10-NEXT:    v_cndmask_b32_e32 v1, v1, v15, vcc_lo
+; GFX10-NEXT:    v_cndmask_b32_e32 v0, v0, v0, vcc_lo
+; GFX10-NEXT:    v_cndmask_b32_e32 v1, v1, v1, vcc_lo
 ; GFX10-NEXT:    s_setpc_b64 s[30:31]
 ;
 ; GFX11-LABEL: dyn_extract_v7f64_v_v:
@@ -2918,7 +2918,7 @@ define double @dyn_extract_v7f64_v_v(<7 x double> %vec, i32 %sel) {
 ; GFX11-NEXT:    v_cmp_eq_u32_e32 vcc_lo, 6, v14
 ; GFX11-NEXT:    v_dual_cndmask_b32 v0, v0, v12 :: v_dual_cndmask_b32 v1, v1, v13
 ; GFX11-NEXT:    v_cmp_eq_u32_e32 vcc_lo, 7, v14
-; GFX11-NEXT:    v_dual_cndmask_b32 v0, v0, v14 :: v_dual_cndmask_b32 v1, v1, v15
+; GFX11-NEXT:    v_dual_cndmask_b32 v0, v0, v0 :: v_dual_cndmask_b32 v1, v1, v1
 ; GFX11-NEXT:    s_setpc_b64 s[30:31]
 entry:
   %ext = extractelement <7 x double> %vec, i32 %sel

llvm/test/CodeGen/AMDGPU/issue92561-restore-undef-scc-verifier-error.ll

@@ -79,9 +79,9 @@ define void @issue92561(ptr addrspace(1) %arg) {
 ; GISEL:       ; %bb.0: ; %bb
 ; GISEL-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
 ; GISEL-NEXT:    s_clause 0x1
-; GISEL-NEXT:    global_load_b128 v[2:5], v[0:1], off
-; GISEL-NEXT:    global_load_b128 v[6:9], v[0:1], off offset:16
-; GISEL-NEXT:    v_mov_b32_e32 v0, 0
+; GISEL-NEXT:    global_load_b128 v[4:7], v[0:1], off
+; GISEL-NEXT:    global_load_b128 v[0:3], v[0:1], off offset:16
+; GISEL-NEXT:    v_mov_b32_e32 v8, 0
 ; GISEL-NEXT:    s_mov_b32 s20, 0
 ; GISEL-NEXT:    s_mov_b32 s3, exec_lo
 ; GISEL-NEXT:    s_mov_b32 s21, s20
@@ -97,49 +97,51 @@ define void @issue92561(ptr addrspace(1) %arg) {
 ; GISEL-NEXT:    s_mov_b32 s11, s20
 ; GISEL-NEXT:    s_waitcnt vmcnt(0)
 ; GISEL-NEXT:  .LBB0_1: ; =>This Inner Loop Header: Depth=1
-; GISEL-NEXT:    v_readfirstlane_b32 s12, v2
-; GISEL-NEXT:    v_readfirstlane_b32 s13, v3
-; GISEL-NEXT:    v_readfirstlane_b32 s14, v4
-; GISEL-NEXT:    v_readfirstlane_b32 s15, v5
-; GISEL-NEXT:    v_readfirstlane_b32 s16, v6
-; GISEL-NEXT:    v_readfirstlane_b32 s17, v7
-; GISEL-NEXT:    v_readfirstlane_b32 s18, v8
-; GISEL-NEXT:    v_readfirstlane_b32 s19, v9
-; GISEL-NEXT:    v_cmp_eq_u64_e32 vcc_lo, s[12:13], v[2:3]
-; GISEL-NEXT:    v_cmp_eq_u64_e64 s0, s[14:15], v[4:5]
-; GISEL-NEXT:    v_cmp_eq_u64_e64 s1, s[16:17], v[6:7]
+; GISEL-NEXT:    v_readfirstlane_b32 s12, v4
+; GISEL-NEXT:    v_readfirstlane_b32 s13, v5
+; GISEL-NEXT:    v_readfirstlane_b32 s14, v6
+; GISEL-NEXT:    v_readfirstlane_b32 s15, v7
+; GISEL-NEXT:    v_readfirstlane_b32 s16, v0
+; GISEL-NEXT:    v_readfirstlane_b32 s17, v1
+; GISEL-NEXT:    v_readfirstlane_b32 s18, v2
+; GISEL-NEXT:    v_readfirstlane_b32 s19, v3
+; GISEL-NEXT:    v_cmp_eq_u64_e32 vcc_lo, s[12:13], v[4:5]
+; GISEL-NEXT:    v_cmp_eq_u64_e64 s0, s[14:15], v[6:7]
+; GISEL-NEXT:    v_cmp_eq_u64_e64 s1, s[16:17], v[0:1]
 ; GISEL-NEXT:    s_delay_alu instid0(VALU_DEP_4) | instskip(NEXT) | instid1(VALU_DEP_3)
-; GISEL-NEXT:    v_cmp_eq_u64_e64 s2, s[18:19], v[8:9]
+; GISEL-NEXT:    v_cmp_eq_u64_e64 s2, s[18:19], v[2:3]
 ; GISEL-NEXT:    s_and_b32 s0, vcc_lo, s0
 ; GISEL-NEXT:    s_delay_alu instid0(VALU_DEP_2) | instid1(SALU_CYCLE_1)
 ; GISEL-NEXT:    s_and_b32 s0, s0, s1
 ; GISEL-NEXT:    s_delay_alu instid0(VALU_DEP_1) | instid1(SALU_CYCLE_1)
 ; GISEL-NEXT:    s_and_b32 s0, s0, s2
 ; GISEL-NEXT:    s_delay_alu instid0(SALU_CYCLE_1)
 ; GISEL-NEXT:    s_and_saveexec_b32 s0, s0
-; GISEL-NEXT:    image_sample_c_lz v1, [v0, v0, v0, v0], s[12:19], s[20:23] dmask:0x1 dim:SQ_RSRC_IMG_2D_ARRAY
-; GISEL-NEXT:    ; implicit-def: $vgpr2_vgpr3_vgpr4_vgpr5_vgpr6_vgpr7_vgpr8_vgpr9
-; GISEL-NEXT:    ; implicit-def: $vgpr0
+; GISEL-NEXT:    image_sample_c_lz v9, [v8, v8, v8, v8], s[12:19], s[20:23] dmask:0x1 dim:SQ_RSRC_IMG_2D_ARRAY
+; GISEL-NEXT:    ; implicit-def: $vgpr4_vgpr5_vgpr6_vgpr7
+; GISEL-NEXT:    ; implicit-def: $vgpr0_vgpr1_vgpr2_vgpr3
+; GISEL-NEXT:    ; implicit-def: $vgpr8
 ; GISEL-NEXT:    s_xor_b32 exec_lo, exec_lo, s0
 ; GISEL-NEXT:    s_cbranch_execnz .LBB0_1
 ; GISEL-NEXT:  ; %bb.2:
 ; GISEL-NEXT:    s_mov_b32 exec_lo, s3
-; GISEL-NEXT:    v_dual_mov_b32 v2, 0 :: v_dual_mov_b32 v3, 1.0
-; GISEL-NEXT:    v_mov_b32_e32 v0, 0x7fc00000
+; GISEL-NEXT:    v_dual_mov_b32 v1, 0 :: v_dual_mov_b32 v0, 0x7fc00000
+; GISEL-NEXT:    v_mov_b32_e32 v2, 1.0
 ; GISEL-NEXT:    s_clause 0x2
-; GISEL-NEXT:    image_sample_c_lz v0, [v2, v2, v0, v2], s[4:11], s[20:23] dmask:0x1 dim:SQ_RSRC_IMG_2D_ARRAY
-; GISEL-NEXT:    image_sample_c_lz v3, [v2, v3, v2, v2], s[4:11], s[20:23] dmask:0x1 dim:SQ_RSRC_IMG_2D_ARRAY
-; GISEL-NEXT:    image_sample_c_lz v4, [v2, v2, v2, v2], s[4:11], s[20:23] dmask:0x1 dim:SQ_RSRC_IMG_2D_ARRAY
+; GISEL-NEXT:    image_sample_c_lz v0, [v1, v1, v0, v1], s[4:11], s[20:23] dmask:0x1 dim:SQ_RSRC_IMG_2D_ARRAY
+; GISEL-NEXT:    image_sample_c_lz v2, [v1, v2, v1, v1], s[4:11], s[20:23] dmask:0x1 dim:SQ_RSRC_IMG_2D_ARRAY
+; GISEL-NEXT:    image_sample_c_lz v3, [v1, v1, v1, v1], s[4:11], s[20:23] dmask:0x1 dim:SQ_RSRC_IMG_2D_ARRAY
 ; GISEL-NEXT:    s_waitcnt vmcnt(2)
-; GISEL-NEXT:    v_add_f32_e32 v0, v1, v0
+; GISEL-NEXT:    v_add_f32_e32 v0, v9, v0
 ; GISEL-NEXT:    s_waitcnt vmcnt(1)
-; GISEL-NEXT:    s_delay_alu instid0(VALU_DEP_1) | instskip(SKIP_1) | instid1(VALU_DEP_1)
-; GISEL-NEXT:    v_dual_add_f32 v0, v3, v0 :: v_dual_mov_b32 v3, v2
+; GISEL-NEXT:    s_delay_alu instid0(VALU_DEP_1) | instskip(SKIP_2) | instid1(VALU_DEP_2)
+; GISEL-NEXT:    v_add_f32_e32 v0, v2, v0
+; GISEL-NEXT:    v_mov_b32_e32 v2, v1
 ; GISEL-NEXT:    s_waitcnt vmcnt(0)
-; GISEL-NEXT:    v_add_f32_e32 v0, v4, v0
+; GISEL-NEXT:    v_add_f32_e32 v0, v3, v0
 ; GISEL-NEXT:    s_delay_alu instid0(VALU_DEP_1)
-; GISEL-NEXT:    v_mul_f32_e32 v1, 0x3e800000, v0
-; GISEL-NEXT:    image_store v[1:3], [v2, v2], s[4:11] dim:SQ_RSRC_IMG_2D unorm
+; GISEL-NEXT:    v_mul_f32_e32 v0, 0x3e800000, v0
+; GISEL-NEXT:    image_store v[0:2], [v1, v1], s[4:11] dim:SQ_RSRC_IMG_2D unorm
 ; GISEL-NEXT:    s_setpc_b64 s[30:31]
 bb:
   %descriptor = load <8 x i32>, ptr addrspace(1) %arg, align 32