[PATCH] D158161: [RISCV] Don't relax policy to ta when vmerge's VL shrinks during folding

[Luke Lau via Phabricator via llvm-commits]

luke updated this revision to Diff 551063.
luke added a comment.

Rebase


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D158161/new/

https://reviews.llvm.org/D158161

Files:
  llvm/lib/Target/RISCV/RISCVISelDAGToDAG.cpp
  llvm/test/CodeGen/RISCV/rvv/fixed-vectors-vselect.ll
  llvm/test/CodeGen/RISCV/rvv/rvv-peephole-vmerge-vops.ll


Index: llvm/test/CodeGen/RISCV/rvv/rvv-peephole-vmerge-vops.ll
===================================================================
--- llvm/test/CodeGen/RISCV/rvv/rvv-peephole-vmerge-vops.ll
+++ llvm/test/CodeGen/RISCV/rvv/rvv-peephole-vmerge-vops.ll
@@ -1065,12 +1065,12 @@
   ret <vscale x 2 x i32> %b
 }
 
-; FIXME: The vadd's new policy should be tail undisturbed since the false op of
-; the vmerge moves from the the body to the tail, and we need to preserve it.
+; The vadd's new policy should be tail undisturbed since the false op of the
+; vmerge moves from the the body to the tail, and we need to preserve it.
 define <vscale x 2 x i32> @vmerge_larger_vl_false_becomes_tail(<vscale x 2 x i32> %false, <vscale x 2 x i32> %x, <vscale x 2 x i32> %y, <vscale x 2 x i1> %m) {
 ; CHECK-LABEL: vmerge_larger_vl_false_becomes_tail:
 ; CHECK:       # %bb.0:
-; CHECK-NEXT:    vsetivli zero, 2, e32, m1, ta, mu
+; CHECK-NEXT:    vsetivli zero, 2, e32, m1, tu, mu
 ; CHECK-NEXT:    vadd.vv v8, v9, v10, v0.t
 ; CHECK-NEXT:    ret
   %a = call <vscale x 2 x i32> @llvm.riscv.vadd.nxv2i32.nxv2i32(<vscale x 2 x i32> poison, <vscale x 2 x i32> %x, <vscale x 2 x i32> %y, i64 2)
Index: llvm/test/CodeGen/RISCV/rvv/fixed-vectors-vselect.ll
===================================================================
--- llvm/test/CodeGen/RISCV/rvv/fixed-vectors-vselect.ll
+++ llvm/test/CodeGen/RISCV/rvv/fixed-vectors-vselect.ll
@@ -28,7 +28,7 @@
 ; RV32-NEXT:    vslidedown.vi v10, v10, 2
 ; RV32-NEXT:    vand.vi v10, v10, 1
 ; RV32-NEXT:    vmsne.vi v0, v10, 0
-; RV32-NEXT:    vsetivli zero, 6, e32, m2, ta, mu
+; RV32-NEXT:    vsetivli zero, 6, e32, m2, tu, mu
 ; RV32-NEXT:    vle32.v v8, (a0), v0.t
 ; RV32-NEXT:    vse32.v v8, (a3)
 ; RV32-NEXT:    ret
@@ -58,7 +58,7 @@
 ; RV64-NEXT:    vslidedown.vi v10, v10, 2
 ; RV64-NEXT:    vand.vi v10, v10, 1
 ; RV64-NEXT:    vmsne.vi v0, v10, 0
-; RV64-NEXT:    vsetivli zero, 6, e32, m2, ta, mu
+; RV64-NEXT:    vsetivli zero, 6, e32, m2, tu, mu
 ; RV64-NEXT:    vle32.v v8, (a0), v0.t
 ; RV64-NEXT:    vse32.v v8, (a3)
 ; RV64-NEXT:    ret
@@ -239,7 +239,7 @@
 ; RV32-NEXT:    vslidedown.vi v10, v10, 2
 ; RV32-NEXT:    vand.vi v10, v10, 1
 ; RV32-NEXT:    vmsne.vi v0, v10, 0
-; RV32-NEXT:    vsetivli zero, 6, e32, m2, ta, mu
+; RV32-NEXT:    vsetivli zero, 6, e32, m2, tu, mu
 ; RV32-NEXT:    vle32.v v8, (a0), v0.t
 ; RV32-NEXT:    vse32.v v8, (a3)
 ; RV32-NEXT:    ret
@@ -269,7 +269,7 @@
 ; RV64-NEXT:    vslidedown.vi v10, v10, 2
 ; RV64-NEXT:    vand.vi v10, v10, 1
 ; RV64-NEXT:    vmsne.vi v0, v10, 0
-; RV64-NEXT:    vsetivli zero, 6, e32, m2, ta, mu
+; RV64-NEXT:    vsetivli zero, 6, e32, m2, tu, mu
 ; RV64-NEXT:    vle32.v v8, (a0), v0.t
 ; RV64-NEXT:    vse32.v v8, (a3)
 ; RV64-NEXT:    ret
Index: llvm/lib/Target/RISCV/RISCVISelDAGToDAG.cpp
===================================================================
--- llvm/lib/Target/RISCV/RISCVISelDAGToDAG.cpp
+++ llvm/lib/Target/RISCV/RISCVISelDAGToDAG.cpp
@@ -3453,6 +3453,7 @@
 
   // Because N and True must have the same merge operand (or True's operand is
   // implicit_def), the "effective" body is the minimum of their VLs.
+  SDValue OrigVL = VL;
   VL = GetMinVL(TrueVL, VL);
   if (!VL)
     return false;
@@ -3500,7 +3501,15 @@
          "Expected instructions with mask have a tied dest.");
 #endif
 
-  uint64_t Policy = isImplicitDef(Merge) ? RISCVII::TAIL_AGNOSTIC : /*TUMU*/ 0;
+  // Use a tumu policy, relaxing it to tail agnostic provided that the merge
+  // operand is undefined.
+  //
+  // However, if the VL became smaller than what the vmerge had originally, then
+  // elements past VL that were previously in the vmerge's body will have moved
+  // to the tail. In that case we always need to use tail undisturbed to
+  // preserve them.
+  bool MergeVLShrunk = VL != OrigVL;
+  uint64_t Policy = (isImplicitDef(Merge) && !MergeVLShrunk) ? RISCVII::TAIL_AGNOSTIC : /*TUMU*/ 0;
   SDValue PolicyOp =
     CurDAG->getTargetConstant(Policy, DL, Subtarget->getXLenVT());
 


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