Author: AZero13 Date: 2026-09-10T03:47:38Z New Revision: 7fe36371c71bb6bef3361c4f7ef081fd2c913f16
URL: https://github.com/llvm/llvm-project/commit/7fe36371c71bb6bef3361c4f7ef081fd2c913f16 DIFF: https://github.com/llvm/llvm-project/commit/7fe36371c71bb6bef3361c4f7ef081fd2c913f16.diff LOG: [RISCV] Fix infinite DAGCombine loop with SETCC and SIGN_EXTEND_INREG (#221593) We generalized (X & -(1 << C1) & 0xffffffff) == C2 << C1 using `sraiw`. The combine generates a `SIGN_EXTEND_INREG` when simplifying. However, when C1 is 0 and the sign bit (bit 31) of X is already known to be zero, `DAGCombiner` sees that `SIGN_EXTEND_INREG` is semantically equivalent to `AND X, 0xFFFFFFFF` (zext). Because `DAGCombiner` considers `AND` to be more canonical than `SIGN_EXTEND_INREG` in this context, it immediately reverts the node back to `AND`. This caused an infinite DAGCombine loop. This patch disables the folding when the C1 is zero. That case is covered by a later combine that already checks if bit 31 is known to be zero. Fixes: https://github.com/llvm/llvm-project/issues/221521 (cherry picked from commit f9a8dec9496fea7c55f591a66a64dbcdc085fc2d) Added: Modified: llvm/lib/Target/RISCV/RISCVISelLowering.cpp llvm/test/CodeGen/RISCV/and-negpow2-cmp.ll Removed: ################################################################################ diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp index 00a13c95d1607..a14637055c36e 100644 --- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp +++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp @@ -18547,7 +18547,7 @@ static SDValue performSETCCCombine(SDNode *N, isPowerOf2_32(-uint32_t(AndRHSInt)) && (N1Int & AndRHSInt) == N1Int) { unsigned ShiftBits = llvm::countr_zero(AndRHSInt); int64_t NewC = SignExtend64<32>(N1Int) >> ShiftBits; - if (NewC >= -2048 && NewC <= 2048) { + if (ShiftBits != 0 && NewC >= -2048 && NewC <= 2048) { SDValue SExt = DAG.getNode(ISD::SIGN_EXTEND_INREG, dl, OpVT, N0.getOperand(0), DAG.getValueType(MVT::i32)); diff --git a/llvm/test/CodeGen/RISCV/and-negpow2-cmp.ll b/llvm/test/CodeGen/RISCV/and-negpow2-cmp.ll index 5bd1edb783fce..50324a100c4c1 100644 --- a/llvm/test/CodeGen/RISCV/and-negpow2-cmp.ll +++ b/llvm/test/CodeGen/RISCV/and-negpow2-cmp.ll @@ -261,3 +261,37 @@ entry: %4 = zext i1 %3 to i64 ret i64 %4 } + +define i64 @PR221593(i1 %0) { +; RV32-LABEL: PR221593: +; RV32: # %bb.0: +; RV32-NEXT: lui a1, 245379 +; RV32-NEXT: slli a0, a0, 31 +; RV32-NEXT: srai a0, a0, 31 +; RV32-NEXT: addi a1, a1, 78 +; RV32-NEXT: lui a2, 3 +; RV32-NEXT: and a3, a0, a1 +; RV32-NEXT: addi a1, a2, -1907 +; RV32-NEXT: seqz a2, a3 +; RV32-NEXT: and a1, a0, a1 +; RV32-NEXT: or a0, a3, a2 +; RV32-NEXT: ret +; +; RV64-LABEL: PR221593: +; RV64: # %bb.0: +; RV64-NEXT: lui a1, %hi(.LCPI13_0) +; RV64-NEXT: ld a1, %lo(.LCPI13_0)(a1) +; RV64-NEXT: slli a0, a0, 63 +; RV64-NEXT: srai a0, a0, 63 +; RV64-NEXT: and a0, a0, a1 +; RV64-NEXT: slli a1, a0, 32 +; RV64-NEXT: seqz a1, a1 +; RV64-NEXT: or a0, a0, a1 +; RV64-NEXT: ret + %2 = select i1 %0, i64 44587060572238, i64 0 + %3 = and i64 %2, 1005072462 + %4 = icmp eq i64 %3, 0 + %5 = zext i1 %4 to i64 + %6 = or i64 %2, %5 + ret i64 %6 +} _______________________________________________ llvm-branch-commits mailing list [email protected] https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-branch-commits
