[llvm] 0e28fd7 - [RISCV] Check the types are the same for folding (sub 0, (setcc x, 0, setlt)) to (sra x, xlen - 1) (#158179)

[via llvm-commits]

Author: Jim Lin
Date: 2025-09-15T09:30:08+08:00
New Revision: 0e28fd7282492669e106617b52494fa4556bb5c4

URL: https://github.com/llvm/llvm-project/commit/0e28fd7282492669e106617b52494fa4556bb5c4
DIFF: https://github.com/llvm/llvm-project/commit/0e28fd7282492669e106617b52494fa4556bb5c4.diff

LOG: [RISCV] Check the types are the same for folding (sub 0, (setcc x, 0, setlt)) to (sra x, xlen - 1) (#158179)

We should check the type of x is the same as `sub` operation. Otherwise
the shift amount xlen -1 will exceed the bit size of x.

Fixes https://github.com/llvm/llvm-project/issues/158121.

Added: 
    llvm/test/CodeGen/RISCV/pr158121.ll

Modified: 
    llvm/lib/Target/RISCV/RISCVISelLowering.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
index f9b484b98739f..5485b916c2031 100644
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -15827,7 +15827,8 @@ static SDValue performSUBCombine(SDNode *N, SelectionDAG &DAG,
   SDValue N1 = N->getOperand(1);
   // fold (sub 0, (setcc x, 0, setlt)) -> (sra x, xlen - 1)
   if (isNullConstant(N0) && N1.getOpcode() == ISD::SETCC && N1.hasOneUse() &&
-      isNullConstant(N1.getOperand(1))) {
+      isNullConstant(N1.getOperand(1)) &&
+      N1.getValueType() == N1.getOperand(0).getValueType()) {
     ISD::CondCode CCVal = cast<CondCodeSDNode>(N1.getOperand(2))->get();
     if (CCVal == ISD::SETLT) {
       SDLoc DL(N);

diff  --git a/llvm/test/CodeGen/RISCV/pr158121.ll b/llvm/test/CodeGen/RISCV/pr158121.ll
new file mode 100644
index 0000000000000..2c018444e9c67
--- /dev/null
+++ b/llvm/test/CodeGen/RISCV/pr158121.ll
@@ -0,0 +1,17 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
+; RUN: llc < %s -mtriple=riscv64 | FileCheck %s
+
+define i64 @f(ptr %p) {
+; CHECK-LABEL: f:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    lb a0, 0(a0)
+; CHECK-NEXT:    srai a0, a0, 63
+; CHECK-NEXT:    ret
+  %load = load i8, ptr %p, align 1
+  %conv1 = zext i8 %load to i32
+  %cmp = icmp ult i32 127, %conv1
+  %conv2 = zext i1 %cmp to i32
+  %sub = sub nsw i32 0, %conv2
+  %conv3 = sext i32 %sub to i64
+  ret i64 %conv3
+}