[VectorCombine] Fix crash in scalarizeVPIntrinsic

[michaelmaitland]

When getSplatOp returns nullptr, the intrinsic cannot be scalarized. This patch includes a test case that fixes a crash from trying to scalarize the VPIntrinsic when getSplatOp returns nullptr. This case can be scalarized in the future by improving getSplatOp, but the checks added in this patch should remain.

This fixes #72034.

[llvmbot]

@llvm/pr-subscribers-llvm-transforms

Author: Michael Maitland (michaelmaitland)

Changes

When getSplatOp returns nullptr, the intrinsic cannot be scalarized. This patch includes a test case that fixes a crash from trying to scalarize the VPIntrinsic when getSplatOp returns nullptr. This case can be scalarized in the future by improving getSplatOp, but the checks added in this patch should remain.

This fixes #72034.

---

Full diff: https://github.com/llvm/llvm-project/pull/72039.diff

2 Files Affected:

• (modified) llvm/lib/Transforms/Vectorize/VectorCombine.cpp (+2)
• (added) llvm/test/Transforms/VectorCombine/RISCV/vpintrin-scalarization-shufflevector-splat.ll (+16)

diff --git a/llvm/lib/Transforms/Vectorize/VectorCombine.cpp b/llvm/lib/Transforms/Vectorize/VectorCombine.cpp
index 9a91ce207bb04c9..6d79c9b13add067 100644
--- a/llvm/lib/Transforms/Vectorize/VectorCombine.cpp
+++ b/llvm/lib/Transforms/Vectorize/VectorCombine.cpp
@@ -843,6 +843,8 @@ bool VectorCombine::scalarizeVPIntrinsic(Instruction &I) {
 
   Value *ScalarOp0 = getSplatValue(Op0);
   Value *ScalarOp1 = getSplatValue(Op1);
+  if (!ScalarOp0 || !ScalarOp1)
+    return false;
   Value *ScalarVal =
       ScalarIntrID
           ? Builder.CreateIntrinsic(VecTy->getScalarType(), *ScalarIntrID,
diff --git a/llvm/test/Transforms/VectorCombine/RISCV/vpintrin-scalarization-shufflevector-splat.ll b/llvm/test/Transforms/VectorCombine/RISCV/vpintrin-scalarization-shufflevector-splat.ll
new file mode 100644
index 000000000000000..d3c477d180aa54f
--- /dev/null
+++ b/llvm/test/Transforms/VectorCombine/RISCV/vpintrin-scalarization-shufflevector-splat.ll
@@ -0,0 +1,16 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 3
+; RUN: opt -S -mtriple=riscv64 -mattr=+v %s -passes=vector-combine | FileCheck %s --check-prefix
+
+declare <4 x i64> @llvm.vp.add.v4i64(<4 x i64>, <4 x i64>, <4 x i1>, i32)
+
+define <4 x i64> @add_v4i64_allonesmask(<4 x i64> %x) {
+; CHECK-LABEL: define <4 x i64> @add_v4i64_allonesmask(
+; CHECK-SAME: <4 x i64> [[X:%.*]]) #[[ATTR1:[0-9]+]] {
+; CHECK-NEXT:    [[TMP1:%.*]] = shufflevector <4 x i64> [[X]], <4 x i64> zeroinitializer, <4 x i32> zeroinitializer
+; CHECK-NEXT:    [[TMP2:%.*]] = call <4 x i64> @llvm.vp.add.v4i64(<4 x i64> [[TMP1]], <4 x i64> zeroinitializer, <4 x i1> <i1 true, i1 true, i1 true, i1 true>, i32 0)
+; CHECK-NEXT:    ret <4 x i64> [[TMP2]]
+;
+  %1 = shufflevector <4 x i64> %x, <4 x i64> zeroinitializer, <4 x i32> zeroinitializer
+  %2 = call <4 x i64> @llvm.vp.add.v4i64(<4 x i64> %1, <4 x i64> zeroinitializer, <4 x i1> <i1 true, i1 true, i1 true, i1 true>, i32 0)
+  ret <4 x i64> %2
+}

[topperc]

Should we use getSplatValue at the top where we used isSplatValue? That way we fail out before we do wasted work.

[michaelmaitland]

Sure. Do you know why getSplatValue fails to get the splat even though isSplatValue returns true? That sounds like a bug to me?

[topperc]

getSplatValue can't create new instructions, it can only return an operand of existing instructions. isSplatValue can look at shuffles and see that it splat one of the elements of its input. To get that element as a scalar you would need to insert an extractelement instruction.

[topperc]

LGTM