[llvm] [LoongArch][MC] Modify branch evaluation for MCInstrAnalysis (PR #73205)

[via llvm-commits]

https://github.com/zhaoqi5 created https://github.com/llvm/llvm-project/pull/73205

Function evaluateBranch() is used to compute target address for a given branch instruction and return true on success. But target address of indirect branch cannot be simply added, so rule it out and just return false.

This patch also add objdump tests which capture the current state of support for printing branch targets. Without this patch, the result of "jirl $zero, $a0, 4" is "jirl $zero, $a0, 4 <foo+0x64>". It is obviously incorrect, because this instruction represents an indirect branch whose target address depends on both the register value and the imm. After this patch, it will be right despite loss of details.

>From 41234629c36b49f394aa17a1cb52151f2855d049 Mon Sep 17 00:00:00 2001
From: zhaoqi <zhaoqi01 at loongson.cn>
Date: Sat, 21 Oct 2023 16:41:14 +0800
Subject: [PATCH] [LoongArch][MC] Modify branch evaluation for MCInstrAnalysis

Function evaluateBranch() is used to compute target address for a given
branch instruction and return true on success. But target address of
indirect branch cannot be simply added, so rule it out and just return
false.

This patch also add objdump tests which capture the current state of
support for printing branch targets. Without this patch, the result of
"jirl $zero, $a0, 4" is "jirl $zero, $a0, 4 <foo+0x64>". It is
obviously incorrect, because this instruction represents an indirect
branch whose target address depends on both the register value and the
imm. After this patch, it will be right despite loss of details.
---
 .../MCTargetDesc/LoongArchMCTargetDesc.cpp    |  3 +-
 .../llvm-objdump/ELF/LoongArch/branches.s     | 76 +++++++++++++++++++
 .../llvm-objdump/ELF/LoongArch/lit.local.cfg  |  2 +
 3 files changed, 80 insertions(+), 1 deletion(-)
 create mode 100644 llvm/test/tools/llvm-objdump/ELF/LoongArch/branches.s
 create mode 100644 llvm/test/tools/llvm-objdump/ELF/LoongArch/lit.local.cfg

diff --git a/llvm/lib/Target/LoongArch/MCTargetDesc/LoongArchMCTargetDesc.cpp b/llvm/lib/Target/LoongArch/MCTargetDesc/LoongArchMCTargetDesc.cpp
index d580c3457fecff8..a4e6a09863e6a68 100644
--- a/llvm/lib/Target/LoongArch/MCTargetDesc/LoongArchMCTargetDesc.cpp
+++ b/llvm/lib/Target/LoongArch/MCTargetDesc/LoongArchMCTargetDesc.cpp
@@ -97,7 +97,8 @@ class LoongArchMCInstrAnalysis : public MCInstrAnalysis {
   bool evaluateBranch(const MCInst &Inst, uint64_t Addr, uint64_t Size,
                       uint64_t &Target) const override {
     unsigned NumOps = Inst.getNumOperands();
-    if (isBranch(Inst) || Inst.getOpcode() == LoongArch::BL) {
+    if ((isBranch(Inst) && !isIndirectBranch(Inst)) ||
+        Inst.getOpcode() == LoongArch::BL) {
       Target = Addr + Inst.getOperand(NumOps - 1).getImm();
       return true;
     }
diff --git a/llvm/test/tools/llvm-objdump/ELF/LoongArch/branches.s b/llvm/test/tools/llvm-objdump/ELF/LoongArch/branches.s
new file mode 100644
index 000000000000000..8cb00aef9954272
--- /dev/null
+++ b/llvm/test/tools/llvm-objdump/ELF/LoongArch/branches.s
@@ -0,0 +1,76 @@
+# RUN: llvm-mc --triple=loongarch32 --filetype=obj < %s | \
+# RUN:   llvm-objdump -d --no-show-raw-insn - | FileCheck %s
+# RUN: llvm-mc --triple=loongarch64 --filetype=obj < %s | \
+# RUN:   llvm-objdump -d --no-show-raw-insn - | FileCheck %s
+
+# CHECK-LABEL: <foo>:
+foo:
+# CHECK: beq $a0, $a1, 108 <foo+0x6c>
+beq $a0, $a1, .Llocal
+# CHECK: bne $a0, $a1, 104 <foo+0x6c>
+bne $a0, $a1, .Llocal
+# CHECK: blt $a0, $a1, 100 <foo+0x6c>
+blt $a0, $a1, .Llocal
+# CHECK: bltu $a0, $a1, 96 <foo+0x6c>
+bltu $a0, $a1, .Llocal
+# CHECK: bge $a0, $a1, 92 <foo+0x6c>
+bge $a0, $a1, .Llocal
+# CHECK: bgeu $a0, $a1, 88 <foo+0x6c>
+bgeu $a0, $a1, .Llocal
+# CHECK: beqz $a0, 84 <foo+0x6c>
+beqz $a0, .Llocal
+# CHECK: bnez $a0, 80 <foo+0x6c>
+bnez $a0, .Llocal
+# CHECK: bceqz $fcc6, 76 <foo+0x6c>
+bceqz $fcc6, .Llocal
+# CHECK: bcnez $fcc6, 72 <foo+0x6c>
+bcnez $fcc6, .Llocal
+
+# CHECK: beq $a0, $a1, 76 <bar>
+beq $a0, $a1, bar
+# CHECK: bne $a0, $a1, 72 <bar>
+bne $a0, $a1, bar
+# CHECK: blt $a0, $a1, 68 <bar>
+blt $a0, $a1, bar
+# CHECK: bltu $a0, $a1, 64 <bar>
+bltu $a0, $a1, bar
+# CHECK: bge $a0, $a1, 60 <bar>
+bge $a0, $a1, bar
+# CHECK: bgeu $a0, $a1, 56 <bar>
+bgeu $a0, $a1, bar
+# CHECK: beqz $a0, 52 <bar>
+beqz $a0, bar
+# CHECK: bnez $a0, 48 <bar>
+bnez $a0, bar
+# CHECK: bceqz $fcc6, 44 <bar>
+bceqz $fcc6, bar
+# CHECK: bcnez $fcc6, 40 <bar>
+bcnez $fcc6, bar
+
+# CHECK: b 28 <foo+0x6c>
+b .Llocal
+# CHECK: b 32 <bar>
+b bar
+
+# CHECK: bl 20 <foo+0x6c>
+bl .Llocal
+# CHECK: bl 24 <bar>
+bl bar
+
+# CHECK: jirl $zero, $a0, 4{{$}}
+jirl $zero, $a0, 4
+# CHECK: jirl $ra, $a0, 4{{$}}
+jirl $ra, $a0, 4
+# CHECK: ret
+ret
+
+.Llocal:
+# CHECK: 6c: nop
+# CHECK: nop
+nop
+nop
+
+# CHECK-LABEL: <bar>:
+bar:
+# CHECK: 74: nop
+nop
diff --git a/llvm/test/tools/llvm-objdump/ELF/LoongArch/lit.local.cfg b/llvm/test/tools/llvm-objdump/ELF/LoongArch/lit.local.cfg
new file mode 100644
index 000000000000000..cc24278acbb414a
--- /dev/null
+++ b/llvm/test/tools/llvm-objdump/ELF/LoongArch/lit.local.cfg
@@ -0,0 +1,2 @@
+if not "LoongArch" in config.root.targets:
+    config.unsupported = True