[llvm] b389adf - [RISCV] Allow non-canonicalized splats in isProfitableToSinkOperands (#161586)

[via llvm-commits]

Author: Philip Reames
Date: 2025-10-01T14:00:28-07:00
New Revision: b389adf56a1610cbdf0aa0a7b0b70b2c6b049f83

URL: https://github.com/llvm/llvm-project/commit/b389adf56a1610cbdf0aa0a7b0b70b2c6b049f83
DIFF: https://github.com/llvm/llvm-project/commit/b389adf56a1610cbdf0aa0a7b0b70b2c6b049f83.diff

LOG: [RISCV] Allow non-canonicalized splats in isProfitableToSinkOperands (#161586)

This isn't an optimization change - IR transforms should have remove the
operands and replaced them with poison. However, I noticed the
non-canonical splat structure in a couple of llvm-reduce outputs. This
results in us creating extremely atypical IR which is quite misleading
about the true cause of what's going on. (Because the non-canonical
splat doesn't get sunk, we then prone whatever was actually holding it
outside the loop in the original example, eliminating insight as to the
true cause of whatever issue we're debugging.)

Added: 
    

Modified: 
    llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp
    llvm/test/CodeGen/RISCV/rvv/sink-splat-operands.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp b/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp
index d4124ae9aeff0..ee25f6918de8b 100644
--- a/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp
+++ b/llvm/lib/Target/RISCV/RISCVTargetTransformInfo.cpp
@@ -3139,8 +3139,8 @@ bool RISCVTTIImpl::isProfitableToSinkOperands(
     bool IsVPSplat = match(Op, m_Intrinsic<Intrinsic::experimental_vp_splat>(
                                    m_Value(), m_Value(), m_Value()));
     if (!IsVPSplat &&
-        !match(Op, m_Shuffle(m_InsertElt(m_Undef(), m_Value(), m_ZeroInt()),
-                             m_Undef(), m_ZeroMask())))
+        !match(Op, m_Shuffle(m_InsertElt(m_Value(), m_Value(), m_ZeroInt()),
+                             m_Value(), m_ZeroMask())))
       continue;
 
     // Don't sink i1 splats.

diff  --git a/llvm/test/CodeGen/RISCV/rvv/sink-splat-operands.ll b/llvm/test/CodeGen/RISCV/rvv/sink-splat-operands.ll
index 02825b2bda484..19a184148c0b6 100644
--- a/llvm/test/CodeGen/RISCV/rvv/sink-splat-operands.ll
+++ b/llvm/test/CodeGen/RISCV/rvv/sink-splat-operands.ll
@@ -6018,3 +6018,39 @@ vector.latch:                                     ; preds = %for.body419
 for.cond.cleanup:                                 ; preds = %vector.latch
   ret void
 }
+
+;; This is exactly like sink_add_splat except that the splat has operands
+;; which haven't been converted to undef.
+define void @sink_non_canonical_splat(ptr nocapture %a, i32 signext %x) {
+; CHECK-LABEL: sink_non_canonical_splat:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    lui a2, 1
+; CHECK-NEXT:    add a2, a0, a2
+; CHECK-NEXT:    vsetivli zero, 4, e32, m1, ta, ma
+; CHECK-NEXT:  .LBB131_1: # %vector.body
+; CHECK-NEXT:    # =>This Inner Loop Header: Depth=1
+; CHECK-NEXT:    vle32.v v8, (a0)
+; CHECK-NEXT:    vadd.vx v8, v8, a1
+; CHECK-NEXT:    vse32.v v8, (a0)
+; CHECK-NEXT:    addi a0, a0, 16
+; CHECK-NEXT:    bne a0, a2, .LBB131_1
+; CHECK-NEXT:  # %bb.2: # %for.cond.cleanup
+; CHECK-NEXT:    ret
+entry:
+  %broadcast.splatinsert = insertelement <4 x i32> zeroinitializer, i32 %x, i32 0
+  %broadcast.splat = shufflevector <4 x i32> %broadcast.splatinsert, <4 x i32> zeroinitializer, <4 x i32> zeroinitializer
+  br label %vector.body
+
+vector.body:                                      ; preds = %vector.body, %entry
+  %index = phi i64 [ 0, %entry ], [ %index.next, %vector.body ]
+  %0 = getelementptr inbounds i32, ptr %a, i64 %index
+  %wide.load = load <4 x i32>, ptr %0, align 4
+  %1 = add <4 x i32> %wide.load, %broadcast.splat
+  store <4 x i32> %1, ptr %0, align 4
+  %index.next = add nuw i64 %index, 4
+  %2 = icmp eq i64 %index.next, 1024
+  br i1 %2, label %for.cond.cleanup, label %vector.body
+
+for.cond.cleanup:                                 ; preds = %vector.body
+  ret void
+}