[PATCH] D116803: [GlobalISel] Use getPreferredShiftAmountTy in one more G_UBFX combine

[Jay Foad via Phabricator via llvm-commits]

foad created this revision.
foad added reviewers: bcahoon, aemerson, arsenm, paquette.
Herald added subscribers: kerbowa, hiraditya, tpr, rovka, nhaehnle, jvesely.
foad requested review of this revision.
Herald added subscribers: llvm-commits, wdng.
Herald added a project: LLVM.

Change CombinerHelper::matchBitfieldExtractFromShrAnd to use
getPreferredShiftAmountTy for the shift-amount-like operands of G_UBFX
just like all the other G_[SU]BFX combines do. This better matches the
AMDGPU legality rules for these instructions.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D116803

Files:
  llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
  llvm/test/CodeGen/AMDGPU/GlobalISel/postlegalizercombiner-ubfx.mir
  llvm/test/CodeGen/AMDGPU/GlobalISel/ubfx.ll


Index: llvm/test/CodeGen/AMDGPU/GlobalISel/ubfx.ll
===================================================================
--- llvm/test/CodeGen/AMDGPU/GlobalISel/ubfx.ll
+++ llvm/test/CodeGen/AMDGPU/GlobalISel/ubfx.ll
@@ -121,22 +121,24 @@
 }
 
 ; Test vector bitfield extract for 64-bits.
+; TODO: No need for a 64-bit shift instruction when the extracted value is
+; entirely contained within the upper or lower half.
 define i64 @v_mask_srl_i64(i64 %value) {
 ; GFX89-LABEL: v_mask_srl_i64:
 ; GFX89:       ; %bb.0:
 ; GFX89-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
-; GFX89-NEXT:    v_and_b32_e32 v0, 0xfe000000, v0
-; GFX89-NEXT:    v_and_b32_e32 v1, 7, v1
 ; GFX89-NEXT:    v_lshrrev_b64 v[0:1], 25, v[0:1]
+; GFX89-NEXT:    v_mov_b32_e32 v1, 0
+; GFX89-NEXT:    v_bfe_u32 v0, v0, 0, 10
 ; GFX89-NEXT:    s_setpc_b64 s[30:31]
 ;
 ; GFX10-LABEL: v_mask_srl_i64:
 ; GFX10:       ; %bb.0:
 ; GFX10-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
 ; GFX10-NEXT:    s_waitcnt_vscnt null, 0x0
-; GFX10-NEXT:    v_and_b32_e32 v0, 0xfe000000, v0
-; GFX10-NEXT:    v_and_b32_e32 v1, 7, v1
 ; GFX10-NEXT:    v_lshrrev_b64 v[0:1], 25, v[0:1]
+; GFX10-NEXT:    v_mov_b32_e32 v1, 0
+; GFX10-NEXT:    v_bfe_u32 v0, v0, 0, 10
 ; GFX10-NEXT:    s_setpc_b64 s[30:31]
  %1 = and i64 %value, 34326183936 ; 1023 << 25
  %2 = lshr i64 %1, 25
@@ -147,10 +149,7 @@
 define amdgpu_ps i64 @s_mask_srl_i64(i64 inreg %value) {
 ; GCN-LABEL: s_mask_srl_i64:
 ; GCN:       ; %bb.0:
-; GCN-NEXT:    s_mov_b32 s2, 0xfe000000
-; GCN-NEXT:    s_mov_b32 s3, 7
-; GCN-NEXT:    s_and_b64 s[0:1], s[0:1], s[2:3]
-; GCN-NEXT:    s_lshr_b64 s[0:1], s[0:1], 25
+; GCN-NEXT:    s_bfe_u64 s[0:1], s[0:1], 0xa0019
 ; GCN-NEXT:    ; return to shader part epilog
  %1 = and i64 %value, 34326183936 ; 1023 << 25
  %2 = lshr i64 %1, 25
Index: llvm/test/CodeGen/AMDGPU/GlobalISel/postlegalizercombiner-ubfx.mir
===================================================================
--- llvm/test/CodeGen/AMDGPU/GlobalISel/postlegalizercombiner-ubfx.mir
+++ llvm/test/CodeGen/AMDGPU/GlobalISel/postlegalizercombiner-ubfx.mir
@@ -145,11 +145,10 @@
     ; GCN: liveins: $vgpr0_vgpr1
     ; GCN-NEXT: {{  $}}
     ; GCN-NEXT: [[COPY:%[0-9]+]]:_(s64) = COPY $vgpr0_vgpr1
-    ; GCN-NEXT: [[C:%[0-9]+]]:_(s64) = G_CONSTANT i64 261888
-    ; GCN-NEXT: [[AND:%[0-9]+]]:_(s64) = G_AND [[COPY]], [[C]]
+    ; GCN-NEXT: [[C:%[0-9]+]]:_(s32) = G_CONSTANT i32 10
     ; GCN-NEXT: [[C1:%[0-9]+]]:_(s32) = G_CONSTANT i32 8
-    ; GCN-NEXT: [[LSHR:%[0-9]+]]:_(s64) = G_LSHR [[AND]], [[C1]](s32)
-    ; GCN-NEXT: $vgpr0_vgpr1 = COPY [[LSHR]](s64)
+    ; GCN-NEXT: [[UBFX:%[0-9]+]]:_(s64) = G_UBFX [[COPY]], [[C1]](s32), [[C]]
+    ; GCN-NEXT: $vgpr0_vgpr1 = COPY [[UBFX]](s64)
     %0:_(s64) = COPY $vgpr0_vgpr1
     %1:_(s64) = G_CONSTANT i64 261888 ; 1023 << 8
     %2:_(s64) = G_AND %0, %1
Index: llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
===================================================================
--- llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
+++ llvm/lib/CodeGen/GlobalISel/CombinerHelper.cpp
@@ -4214,8 +4214,9 @@
 
   const Register Dst = MI.getOperand(0).getReg();
   LLT Ty = MRI.getType(Dst);
+  LLT ExtractTy = getTargetLowering().getPreferredShiftAmountTy(Ty);
   if (!getTargetLowering().isConstantUnsignedBitfieldExtractLegal(
-          TargetOpcode::G_UBFX, Ty, Ty))
+          TargetOpcode::G_UBFX, Ty, ExtractTy))
     return false;
 
   // Try to match shr (and x, c1), c2
@@ -4249,8 +4250,8 @@
     return false;
 
   MatchInfo = [=](MachineIRBuilder &B) {
-    auto WidthCst = B.buildConstant(Ty, Width);
-    auto PosCst = B.buildConstant(Ty, Pos);
+    auto WidthCst = B.buildConstant(ExtractTy, Width);
+    auto PosCst = B.buildConstant(ExtractTy, Pos);
     B.buildInstr(TargetOpcode::G_UBFX, {Dst}, {AndSrc, PosCst, WidthCst});
   };
   return true;


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