[llvm] 3710050 - [RISCV][VLOPT] Set CommonVL as the largest of the users (#120349)

[via llvm-commits]

Author: Michael Maitland
Date: 2024-12-19T13:22:31-05:00
New Revision: 37100505664a4c451eb530bc899de204adb80a13

URL: https://github.com/llvm/llvm-project/commit/37100505664a4c451eb530bc899de204adb80a13
DIFF: https://github.com/llvm/llvm-project/commit/37100505664a4c451eb530bc899de204adb80a13.diff

LOG: [RISCV][VLOPT] Set CommonVL as the largest of the users (#120349)

Prior to this patch, we required that all users had the same VL in order
to optimize. But as the FIXME said, we can use the largest VL to
optimize, as long as we can determine what the largest is. This patch
implements the FIXME.

Added: 
    

Modified: 
    llvm/lib/Target/RISCV/RISCVVLOptimizer.cpp
    llvm/test/CodeGen/RISCV/rvv/vl-opt.mir

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Target/RISCV/RISCVVLOptimizer.cpp b/llvm/lib/Target/RISCV/RISCVVLOptimizer.cpp
index eefbad7460d1bd..4e3212c70ee9b0 100644
--- a/llvm/lib/Target/RISCV/RISCVVLOptimizer.cpp
+++ b/llvm/lib/Target/RISCV/RISCVVLOptimizer.cpp
@@ -973,13 +973,13 @@ bool RISCVVLOptimizer::checkUsers(const MachineOperand *&CommonVL,
     assert((!VLOp.isReg() || VLOp.getReg() != RISCV::X0) &&
            "Did not expect X0 VL");
 
-    if (!CommonVL) {
+    // Use the largest VL among all the users. If we cannot determine this
+    // statically, then we cannot optimize the VL.
+    if (!CommonVL || RISCV::isVLKnownLE(*CommonVL, VLOp)) {
       CommonVL = &VLOp;
       LLVM_DEBUG(dbgs() << "    User VL is: " << VLOp << "\n");
-    } else if (!CommonVL->isIdenticalTo(VLOp)) {
-      // FIXME: This check requires all users to have the same VL. We can relax
-      // this and get the largest VL amongst all users.
-      LLVM_DEBUG(dbgs() << "    Abort because users have 
diff erent VL\n");
+    } else if (!RISCV::isVLKnownLE(VLOp, *CommonVL)) {
+      LLVM_DEBUG(dbgs() << "    Abort because cannot determine a common VL\n");
       CanReduceVL = false;
       break;
     }

diff  --git a/llvm/test/CodeGen/RISCV/rvv/vl-opt.mir b/llvm/test/CodeGen/RISCV/rvv/vl-opt.mir
index 010e3ca642269b..3f966b036589fd 100644
--- a/llvm/test/CodeGen/RISCV/rvv/vl-opt.mir
+++ b/llvm/test/CodeGen/RISCV/rvv/vl-opt.mir
@@ -33,3 +33,81 @@ body: |
     %y:vr = PseudoVREDSUM_VS_M1_E64 $noreg, %x, $noreg, -1, 6 /* e64 */, 0 /* tu, mu */
     %z:vr = PseudoVADD_VV_M1 $noreg, %x, $noreg, %vl, 5 /* e32 */, 0 /* tu, mu */
 ...
+---
+name: use_largest_common_vl_imm_imm
+body: |
+  bb.0:
+    ; CHECK-LABEL: name: use_largest_common_vl_imm_imm
+    ; CHECK: %x:vr = PseudoVADD_VV_M1 $noreg, $noreg, $noreg, 2, 3 /* e8 */, 0 /* tu, mu */
+    ; CHECK-NEXT: %y:vr = PseudoVADD_VV_M1 $noreg, %x, $noreg, 1, 3 /* e8 */, 0 /* tu, mu */
+    ; CHECK-NEXT: %z:vr = PseudoVADD_VV_M1 $noreg, %x, $noreg, 2, 3 /* e8 */, 0 /* tu, mu */
+    %x:vr = PseudoVADD_VV_M1 $noreg, $noreg, $noreg, -1, 3 /* e8 */, 0
+    %y:vr = PseudoVADD_VV_M1 $noreg, %x, $noreg, 1, 3 /* e8 */, 0
+    %z:vr = PseudoVADD_VV_M1 $noreg, %x, $noreg, 2, 3 /* e8 */, 0
+...
+---
+name: use_largest_common_vl_same_reg
+body: |
+  bb.0:
+    liveins: $x1
+    ; CHECK-LABEL: name: use_largest_common_vl_same_reg
+    ; CHECK: liveins: $x1
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: %vl:gprnox0 = COPY $x1
+    ; CHECK-NEXT: %x:vr = PseudoVADD_VV_M1 $noreg, $noreg, $noreg, %vl, 3 /* e8 */, 0 /* tu, mu */
+    ; CHECK-NEXT: %y:vr = PseudoVADD_VV_M1 $noreg, %x, $noreg, %vl, 3 /* e8 */, 0 /* tu, mu */
+    ; CHECK-NEXT: %z:vr = PseudoVADD_VV_M1 $noreg, %x, $noreg, %vl, 3 /* e8 */, 0 /* tu, mu */
+    %vl:gprnox0 = COPY $x1
+    %x:vr = PseudoVADD_VV_M1 $noreg, $noreg, $noreg, -1, 3 /* e8 */, 0
+    %y:vr = PseudoVADD_VV_M1 $noreg, %x, $noreg, %vl, 3 /* e8 */, 0
+    %z:vr = PseudoVADD_VV_M1 $noreg, %x, $noreg, %vl, 3 /* e8 */, 0
+...
+---
+name: use_largest_common_vl_
diff _regs
+body: |
+  bb.0:
+    liveins: $x1, $x2
+    ; CHECK-LABEL: name: use_largest_common_vl_
diff _regs
+    ; CHECK: liveins: $x1, $x2
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: %vl0:gprnox0 = COPY $x1
+    ; CHECK-NEXT: %vl1:gprnox0 = COPY $x2
+    ; CHECK-NEXT: %x:vr = PseudoVADD_VV_M1 $noreg, $noreg, $noreg, -1, 3 /* e8 */, 0 /* tu, mu */
+    ; CHECK-NEXT: %y:vr = PseudoVADD_VV_M1 $noreg, %x, $noreg, %vl0, 3 /* e8 */, 0 /* tu, mu */
+    ; CHECK-NEXT: %z:vr = PseudoVADD_VV_M1 $noreg, %x, $noreg, %vl1, 3 /* e8 */, 0 /* tu, mu */
+    %vl0:gprnox0 = COPY $x1
+    %vl1:gprnox0 = COPY $x2
+    %x:vr = PseudoVADD_VV_M1 $noreg, $noreg, $noreg, -1, 3 /* e8 */, 0
+    %y:vr = PseudoVADD_VV_M1 $noreg, %x, $noreg, %vl0, 3 /* e8 */, 0
+    %z:vr = PseudoVADD_VV_M1 $noreg, %x, $noreg, %vl1, 3 /* e8 */, 0
+...
+---
+name: use_largest_common_vl_imm_reg
+body: |
+  bb.0:
+    liveins: $x1
+    ; CHECK-LABEL: name: use_largest_common_vl_imm_reg
+    ; CHECK: liveins: $x1
+    ; CHECK-NEXT: {{  $}}
+    ; CHECK-NEXT: %vl:gprnox0 = COPY $x1
+    ; CHECK-NEXT: %x:vr = PseudoVADD_VV_M1 $noreg, $noreg, $noreg, -1, 3 /* e8 */, 0 /* tu, mu */
+    ; CHECK-NEXT: %y:vr = PseudoVADD_VV_M1 $noreg, %x, $noreg, %vl, 3 /* e8 */, 0 /* tu, mu */
+    ; CHECK-NEXT: %z:vr = PseudoVADD_VV_M1 $noreg, %x, $noreg, 1, 3 /* e8 */, 0 /* tu, mu */
+    %vl:gprnox0 = COPY $x1
+    %x:vr = PseudoVADD_VV_M1 $noreg, $noreg, $noreg, -1, 3 /* e8 */, 0
+    %y:vr = PseudoVADD_VV_M1 $noreg, %x, $noreg, %vl, 3 /* e8 */, 0
+    %z:vr = PseudoVADD_VV_M1 $noreg, %x, $noreg, 1, 3 /* e8 */, 0
+...
+---
+name: use_largest_common_vl_imm_vlmax
+body: |
+  bb.0:
+    ; CHECK-LABEL: name: use_largest_common_vl_imm_vlmax
+    ; CHECK: %x:vr = PseudoVADD_VV_M1 $noreg, $noreg, $noreg, -1, 3 /* e8 */, 0 /* tu, mu */
+    ; CHECK-NEXT: %y:vr = PseudoVADD_VV_M1 $noreg, %x, $noreg, 1, 3 /* e8 */, 0 /* tu, mu */
+    ; CHECK-NEXT: %z:vr = PseudoVADD_VV_M1 $noreg, %x, $noreg, -1, 3 /* e8 */, 0 /* tu, mu */
+    %x:vr = PseudoVADD_VV_M1 $noreg, $noreg, $noreg, -1, 3 /* e8 */, 0
+    %y:vr = PseudoVADD_VV_M1 $noreg, %x, $noreg, 1, 3 /* e8 */, 0
+    %z:vr = PseudoVADD_VV_M1 $noreg, %x, $noreg, -1, 3 /* e8 */, 0
+...
+