Clang fails when building LLVM for RISCV

[kongy]

fatal error: error in backend: Do not know how to split the result of this operator!

Reduced reproducer attached.

reduce.zip

[llvmbot]

@llvm/issue-subscribers-backend-risc-v

Author: Yi Kong (kongy)

`fatal error: error in backend: Do not know how to split the result of this operator!`

Reduced reproducer attached.

reduce.zip

[topperc]

Looks like #66800 is missing a check for legal type.

[topperc]

Possible fix

diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
index 27037f4d5c5c..405d99f14d8f 100644
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -15812,7 +15812,8 @@ SDValue RISCVTargetLowering::PerformDAGCombine(SDNode *N,
           MGN->getMemOperand(), IndexType, MGN->getExtensionType());
 
     if (Index.getOpcode() == ISD::BUILD_VECTOR &&
-        MGN->getExtensionType() == ISD::NON_EXTLOAD) {
+        MGN->getExtensionType() == ISD::NON_EXTLOAD &&
+        isTypeLegal(VT)) {
       if (std::optional<VIDSequence> SimpleVID = isSimpleVIDSequence(Index);
           SimpleVID && SimpleVID->StepDenominator == 1) {
         const int64_t StepNumerator = SimpleVID->StepNumerator;

[lukel97]

Possible fix

diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
index 27037f4d5c5c..405d99f14d8f 100644
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -15812,7 +15812,8 @@ SDValue RISCVTargetLowering::PerformDAGCombine(SDNode *N,
           MGN->getMemOperand(), IndexType, MGN->getExtensionType());
 
     if (Index.getOpcode() == ISD::BUILD_VECTOR &&
-        MGN->getExtensionType() == ISD::NON_EXTLOAD) {
+        MGN->getExtensionType() == ISD::NON_EXTLOAD &&
+        isTypeLegal(VT)) {
       if (std::optional<VIDSequence> SimpleVID = isSimpleVIDSequence(Index);
           SimpleVID && SimpleVID->StepDenominator == 1) {
         const int64_t StepNumerator = SimpleVID->StepNumerator;

This fixes it on my end. And the combine kicks in again once the MGATHER has been split, so we end up with 2 v16i64 vlse64s from the one v32i64 it was crashing on.

[topperc]

@lukel97 can you make a PR?