[llvm] [RISCV] Don't create BuildPairF64 or SplitF64 nodes without D or Zdinx. (PR #116159)

[Craig Topper via llvm-commits]

https://github.com/topperc created https://github.com/llvm/llvm-project/pull/116159

The fix in ReplaceNodeResults is the only one really required for the known crash.

I couldn't hit the case in LowerOperation because that requires (f64 (bitcast i64)), but the result type is softened before the input so we don't get a chance to legalize the input.

The change to the setOperationAction call was an observation that a i64<->vector cast should not be custom legalized on RV32. The custom code already calls isTypeLegal on the scalar type.

>From cbfcbd3f8cc16f3ad1f3df499a555377af039d37 Mon Sep 17 00:00:00 2001
From: Greg Roth <grroth at microsoft.com>
Date: Wed, 13 Nov 2024 17:44:54 -0700
Subject: [PATCH] [RISCV] Don't create BuildPairF64 or SplitF64 nodes without D
 or Zdinx.

The fix in ReplaceNodeResults is the only one really required for
the known crash.

I couldn't hit the case in LowerOperation because that requires
(f64 (bitcast i64)), but the result type is softened before
the input so we don't get a chance to legalize the input.

The change to the setOperationAction call was an observation that
a i64<->vector cast should not be custom legalized on RV32. The
custom code already calls isTypeLegal on the scalar type.
---
 llvm/lib/Target/RISCV/RISCVISelLowering.cpp   | 10 +++++---
 .../RISCV/rvv/rv32-zve-bitcast-crash.ll       | 24 +++++++++++++++++++
 2 files changed, 31 insertions(+), 3 deletions(-)
 create mode 100644 llvm/test/CodeGen/RISCV/rvv/rv32-zve-bitcast-crash.ll

diff --git a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
index 3df8eca8cae7fb..706952925c1183 100644
--- a/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
+++ b/llvm/lib/Target/RISCV/RISCVISelLowering.cpp
@@ -1438,8 +1438,10 @@ RISCVTargetLowering::RISCVTargetLowering(const TargetMachine &TM,
       }
 
       // Custom-legalize bitcasts from fixed-length vectors to scalar types.
-      setOperationAction(ISD::BITCAST, {MVT::i8, MVT::i16, MVT::i32, MVT::i64},
+      setOperationAction(ISD::BITCAST, {MVT::i8, MVT::i16, MVT::i32},
                          Custom);
+      if (Subtarget.is64Bit())
+        setOperationAction(ISD::BITCAST, MVT::i64, Custom);
       if (Subtarget.hasStdExtZfhminOrZhinxmin())
         setOperationAction(ISD::BITCAST, MVT::f16, Custom);
       if (Subtarget.hasStdExtZfbfmin())
@@ -6422,7 +6424,8 @@ SDValue RISCVTargetLowering::LowerOperation(SDValue Op,
       SDValue NewOp0 = DAG.getNode(ISD::ANY_EXTEND, DL, MVT::i64, Op0);
       return DAG.getNode(RISCVISD::FMV_W_X_RV64, DL, MVT::f32, NewOp0);
     }
-    if (VT == MVT::f64 && Op0VT == MVT::i64 && XLenVT == MVT::i32) {
+    if (VT == MVT::f64 && Op0VT == MVT::i64 && XLenVT == MVT::i32 &&
+        Subtarget.hasStdExtDOrZdinx()) {
       SDValue Lo, Hi;
       std::tie(Lo, Hi) = DAG.SplitScalar(Op0, DL, MVT::i32, MVT::i32);
       return DAG.getNode(RISCVISD::BuildPairF64, DL, MVT::f64, Lo, Hi);
@@ -12940,7 +12943,8 @@ void RISCVTargetLowering::ReplaceNodeResults(SDNode *N,
       SDValue FPConv =
           DAG.getNode(RISCVISD::FMV_X_ANYEXTW_RV64, DL, MVT::i64, Op0);
       Results.push_back(DAG.getNode(ISD::TRUNCATE, DL, MVT::i32, FPConv));
-    } else if (VT == MVT::i64 && Op0VT == MVT::f64 && XLenVT == MVT::i32) {
+    } else if (VT == MVT::i64 && Op0VT == MVT::f64 && XLenVT == MVT::i32 &&
+               Subtarget.hasStdExtDOrZdinx()) {
       SDValue NewReg = DAG.getNode(RISCVISD::SplitF64, DL,
                                    DAG.getVTList(MVT::i32, MVT::i32), Op0);
       SDValue RetReg = DAG.getNode(ISD::BUILD_PAIR, DL, MVT::i64,
diff --git a/llvm/test/CodeGen/RISCV/rvv/rv32-zve-bitcast-crash.ll b/llvm/test/CodeGen/RISCV/rvv/rv32-zve-bitcast-crash.ll
new file mode 100644
index 00000000000000..0749aab9b5e80d
--- /dev/null
+++ b/llvm/test/CodeGen/RISCV/rvv/rv32-zve-bitcast-crash.ll
@@ -0,0 +1,24 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 4
+; RUN: llc < %s -mtriple=riscv32 -mattr=+zve32f,+zvl128b | FileCheck %s
+
+; This bitcast previously incorrectly produce a SplitF64 node.
+
+define i64 @foo(double %x) {
+; CHECK-LABEL: foo:
+; CHECK:       # %bb.0:
+; CHECK-NEXT:    addi sp, sp, -16
+; CHECK-NEXT:    .cfi_def_cfa_offset 16
+; CHECK-NEXT:    sw ra, 12(sp) # 4-byte Folded Spill
+; CHECK-NEXT:    .cfi_offset ra, -4
+; CHECK-NEXT:    lui a3, 261888
+; CHECK-NEXT:    li a2, 0
+; CHECK-NEXT:    call __adddf3
+; CHECK-NEXT:    lw ra, 12(sp) # 4-byte Folded Reload
+; CHECK-NEXT:    .cfi_restore ra
+; CHECK-NEXT:    addi sp, sp, 16
+; CHECK-NEXT:    .cfi_def_cfa_offset 0
+; CHECK-NEXT:    ret
+  %a = fadd double %x, 1.0
+  %b = bitcast double %a to i64
+  ret i64 %b
+}