[llvm] [RISCV} Don't delete all fixups in RISCVMCCodeEmitter::expandLongCondBr. (PR #109513)

[Craig Topper via llvm-commits]

https://github.com/topperc created https://github.com/llvm/llvm-project/pull/109513

The Fixups vector passed into this function may already have fixups in it from earlier instructions. We should not erase those. We just want to erase fixups added by this function.

Fixes #108612.

>From 9b05a6f097cef7acc59d9266f464a7d14142943e Mon Sep 17 00:00:00 2001
From: Craig Topper <craig.topper at sifive.com>
Date: Fri, 20 Sep 2024 21:50:08 -0700
Subject: [PATCH] [RISCV} Don't delete all fixups in
 RISCVMCCodeEmitter::expandLongCondBr.

The Fixups vector passed into this function may already have fixups
in it from earlier instructions. We should not erase those. We
just want to erase fixups added by this function.

Fixes #108612.
---
 .../RISCV/MCTargetDesc/RISCVMCCodeEmitter.cpp |  7 ++++++-
 .../MC/RISCV/long-conditional-jump-crash.s    | 19 +++++++++++++++++++
 2 files changed, 25 insertions(+), 1 deletion(-)
 create mode 100644 llvm/test/MC/RISCV/long-conditional-jump-crash.s

diff --git a/llvm/lib/Target/RISCV/MCTargetDesc/RISCVMCCodeEmitter.cpp b/llvm/lib/Target/RISCV/MCTargetDesc/RISCVMCCodeEmitter.cpp
index 75323632dd5333..66394dc8cd138b 100644
--- a/llvm/lib/Target/RISCV/MCTargetDesc/RISCVMCCodeEmitter.cpp
+++ b/llvm/lib/Target/RISCV/MCTargetDesc/RISCVMCCodeEmitter.cpp
@@ -283,13 +283,18 @@ void RISCVMCCodeEmitter::expandLongCondBr(const MCInst &MI,
     Offset = 4;
   }
 
+  // Save the number fixups.
+  size_t N = Fixups.size();
+
   // Emit an unconditional jump to the destination.
   MCInst TmpInst =
       MCInstBuilder(RISCV::JAL).addReg(RISCV::X0).addOperand(SrcSymbol);
   uint32_t Binary = getBinaryCodeForInstr(TmpInst, Fixups, STI);
   support::endian::write(CB, Binary, llvm::endianness::little);
 
-  Fixups.clear();
+  // Drop any fixup added so we can add the correct one.
+  Fixups.resize(N);
+
   if (SrcSymbol.isExpr()) {
     Fixups.push_back(MCFixup::create(Offset, SrcSymbol.getExpr(),
                                      MCFixupKind(RISCV::fixup_riscv_jal),
diff --git a/llvm/test/MC/RISCV/long-conditional-jump-crash.s b/llvm/test/MC/RISCV/long-conditional-jump-crash.s
new file mode 100644
index 00000000000000..bac0036ca5568f
--- /dev/null
+++ b/llvm/test/MC/RISCV/long-conditional-jump-crash.s
@@ -0,0 +1,19 @@
+# RUN: llvm-mc %s -mc-relax-all -triple=riscv64 -filetype=obj \
+# RUN:     | llvm-objdump -d -M no-aliases - \
+# RUN:     | FileCheck --check-prefix=CHECK %s
+
+# This test previously crashed because expanding a conditional branch deleted
+# all fixups in the fragment.
+
+# CHECK:      beq     s0, zero, 0x8
+# CHECK-NEXT: jal     zero, 0x14
+# CHECK-NEXT: jal     zero, 0x14
+# CHECK-NEXT: bne     s0, zero, 0x14
+# CHECK-NEXT: jal     zero, 0x14
+
+# CHECK:      jalr    zero, 0x0(ra)
+  bnez s0, .foo
+  j    .foo
+  beqz s0, .foo
+.foo:
+  ret