[PATCH] D125133: [riscv] Fix state tracking bug on vsetvli (phi of vsetvli) peephole

[Philip Reames via Phabricator via llvm-commits]

This revision was landed with ongoing or failed builds.
This revision was automatically updated to reflect the committed changes.
Closed by commit rG7ed16e7c510a: [riscv] Fix state tracking bug on vsetvli (phi of vsetvli) peephole (authored by reames).

Changed prior to commit:
  https://reviews.llvm.org/D125133?vs=427746&id=428061#toc

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D125133/new/

https://reviews.llvm.org/D125133

Files:
  llvm/lib/Target/RISCV/RISCVInsertVSETVLI.cpp
  llvm/test/CodeGen/RISCV/rvv/vsetvli-insert-crossbb.ll


Index: llvm/test/CodeGen/RISCV/rvv/vsetvli-insert-crossbb.ll
===================================================================
--- llvm/test/CodeGen/RISCV/rvv/vsetvli-insert-crossbb.ll
+++ llvm/test/CodeGen/RISCV/rvv/vsetvli-insert-crossbb.ll
@@ -453,7 +453,7 @@
 ; CHECK-NEXT:    vle32.v v16, (a2)
 ; CHECK-NEXT:    slli a4, a3, 2
 ; CHECK-NEXT:    add a1, a1, a4
-; CHECK-NEXT:    vsetvli zero, a3, e32, m8, tu, mu
+; CHECK-NEXT:    vsetvli zero, zero, e32, m8, tu, mu
 ; CHECK-NEXT:    vfmacc.vf v16, fa0, v8
 ; CHECK-NEXT:    vse32.v v16, (a2)
 ; CHECK-NEXT:    sub a0, a0, a3
Index: llvm/lib/Target/RISCV/RISCVInsertVSETVLI.cpp
===================================================================
--- llvm/lib/Target/RISCV/RISCVInsertVSETVLI.cpp
+++ llvm/lib/Target/RISCV/RISCVInsertVSETVLI.cpp
@@ -1124,9 +1124,16 @@
         // use the predecessor information.
         assert(BlockInfo[MBB.getNumber()].Pred.isValid() &&
                "Expected a valid predecessor state.");
-        if (needVSETVLI(NewInfo, BlockInfo[MBB.getNumber()].Pred) &&
-            needVSETVLIPHI(NewInfo, MBB)) {
-          insertVSETVLI(MBB, MI, NewInfo, BlockInfo[MBB.getNumber()].Pred);
+        if (needVSETVLI(NewInfo, BlockInfo[MBB.getNumber()].Pred)) {
+          // If this is the first implicit state change, and the state change
+          // requested can be proven to produce the same register contents, we
+          // can skip emitting the actual state change and continue as if we
+          // had since we know the GPR result of the implicit state change
+          // wouldn't be used and VL/VTYPE registers are correct.  Note that
+          // we *do* need to model the state as if it changed as while the
+          // register contents are unchanged, the abstract model can change.
+          if (needVSETVLIPHI(NewInfo, MBB))
+            insertVSETVLI(MBB, MI, NewInfo, BlockInfo[MBB.getNumber()].Pred);
           CurInfo = NewInfo;
         }
       } else {


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