[PATCH] D138050: AMDGPU/GlobalISel: Insert freeze when splitting vector G_SEXT_INREG

[Matt Arsenault via Phabricator via llvm-commits]

arsenm updated this revision to Diff 475886.
arsenm added a comment.

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CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D138050/new/

https://reviews.llvm.org/D138050

Files:
  llvm/lib/Target/AMDGPU/AMDGPURegisterBankInfo.cpp
  llvm/test/CodeGen/AMDGPU/GlobalISel/regbankselect-sext-inreg.mir


Index: llvm/test/CodeGen/AMDGPU/GlobalISel/regbankselect-sext-inreg.mir
===================================================================
--- llvm/test/CodeGen/AMDGPU/GlobalISel/regbankselect-sext-inreg.mir
+++ llvm/test/CodeGen/AMDGPU/GlobalISel/regbankselect-sext-inreg.mir
@@ -135,7 +135,8 @@
     ; CHECK-NEXT: {{  $}}
     ; CHECK-NEXT: [[COPY:%[0-9]+]]:vgpr(s64) = COPY $vgpr0_vgpr1
     ; CHECK-NEXT: [[UV:%[0-9]+]]:vgpr(s32), [[UV1:%[0-9]+]]:vgpr(s32) = G_UNMERGE_VALUES [[COPY]](s64)
-    ; CHECK-NEXT: [[SEXT_INREG:%[0-9]+]]:vgpr(s32) = G_SEXT_INREG [[UV]], 1
+    ; CHECK-NEXT: [[FREEZE:%[0-9]+]]:vgpr(s32) = G_FREEZE [[UV]]
+    ; CHECK-NEXT: [[SEXT_INREG:%[0-9]+]]:vgpr(s32) = G_SEXT_INREG [[FREEZE]], 1
     ; CHECK-NEXT: [[C:%[0-9]+]]:vgpr(s32) = G_CONSTANT i32 31
     ; CHECK-NEXT: [[ASHR:%[0-9]+]]:vgpr(s32) = G_ASHR [[SEXT_INREG]], [[C]](s32)
     ; CHECK-NEXT: [[MV:%[0-9]+]]:vgpr(s64) = G_MERGE_VALUES [[SEXT_INREG]](s32), [[ASHR]](s32)
@@ -159,7 +160,8 @@
     ; CHECK-NEXT: {{  $}}
     ; CHECK-NEXT: [[COPY:%[0-9]+]]:vgpr(s64) = COPY $vgpr0_vgpr1
     ; CHECK-NEXT: [[UV:%[0-9]+]]:vgpr(s32), [[UV1:%[0-9]+]]:vgpr(s32) = G_UNMERGE_VALUES [[COPY]](s64)
-    ; CHECK-NEXT: [[SEXT_INREG:%[0-9]+]]:vgpr(s32) = G_SEXT_INREG [[UV]], 31
+    ; CHECK-NEXT: [[FREEZE:%[0-9]+]]:vgpr(s32) = G_FREEZE [[UV]]
+    ; CHECK-NEXT: [[SEXT_INREG:%[0-9]+]]:vgpr(s32) = G_SEXT_INREG [[FREEZE]], 31
     ; CHECK-NEXT: [[C:%[0-9]+]]:vgpr(s32) = G_CONSTANT i32 31
     ; CHECK-NEXT: [[ASHR:%[0-9]+]]:vgpr(s32) = G_ASHR [[SEXT_INREG]], [[C]](s32)
     ; CHECK-NEXT: [[MV:%[0-9]+]]:vgpr(s64) = G_MERGE_VALUES [[SEXT_INREG]](s32), [[ASHR]](s32)
@@ -183,10 +185,10 @@
     ; CHECK-NEXT: {{  $}}
     ; CHECK-NEXT: [[COPY:%[0-9]+]]:vgpr(s64) = COPY $vgpr0_vgpr1
     ; CHECK-NEXT: [[UV:%[0-9]+]]:vgpr(s32), [[UV1:%[0-9]+]]:vgpr(s32) = G_UNMERGE_VALUES [[COPY]](s64)
-    ; CHECK-NEXT: [[COPY1:%[0-9]+]]:vgpr(s32) = COPY [[UV]](s32)
+    ; CHECK-NEXT: [[FREEZE:%[0-9]+]]:vgpr(s32) = G_FREEZE [[UV]]
     ; CHECK-NEXT: [[C:%[0-9]+]]:vgpr(s32) = G_CONSTANT i32 31
-    ; CHECK-NEXT: [[ASHR:%[0-9]+]]:vgpr(s32) = G_ASHR [[COPY1]], [[C]](s32)
-    ; CHECK-NEXT: [[MV:%[0-9]+]]:vgpr(s64) = G_MERGE_VALUES [[COPY1]](s32), [[ASHR]](s32)
+    ; CHECK-NEXT: [[ASHR:%[0-9]+]]:vgpr(s32) = G_ASHR [[FREEZE]], [[C]](s32)
+    ; CHECK-NEXT: [[MV:%[0-9]+]]:vgpr(s64) = G_MERGE_VALUES [[FREEZE]](s32), [[ASHR]](s32)
     ; CHECK-NEXT: S_ENDPGM 0, implicit [[MV]](s64)
     %0:_(s64) = COPY $vgpr0_vgpr1
     %1:_(s64) = G_SEXT_INREG %0, 32
Index: llvm/lib/Target/AMDGPU/AMDGPURegisterBankInfo.cpp
===================================================================
--- llvm/lib/Target/AMDGPU/AMDGPURegisterBankInfo.cpp
+++ llvm/lib/Target/AMDGPU/AMDGPURegisterBankInfo.cpp
@@ -2447,17 +2447,21 @@
 
     int Amt = MI.getOperand(2).getImm();
     if (Amt <= 32) {
+      // Downstream users have expectations for the high bit behavior, so freeze
+      // incoming poison.
       if (Amt == 32) {
         // The low bits are unchanged.
-        B.buildCopy(DstRegs[0], SrcRegs[0]);
+        B.buildFreeze(DstRegs[0], SrcRegs[0]);
       } else {
+        auto Freeze = B.buildFreeze(S32, SrcRegs[0]);
         // Extend in the low bits and propagate the sign bit to the high half.
-        B.buildSExtInReg(DstRegs[0], SrcRegs[0], Amt);
+        B.buildSExtInReg(DstRegs[0], Freeze, Amt);
       }
 
       B.buildAShr(DstRegs[1], DstRegs[0], B.buildConstant(S32, 31));
     } else {
       // The low bits are unchanged, and extend in the high bits.
+      // No freeze required
       B.buildCopy(DstRegs[0], SrcRegs[0]);
       B.buildSExtInReg(DstRegs[1], DstRegs[0], Amt - 32);
     }


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