[llvm] [BOLT][RISCV] Use target features from object file (PR #69836)

[Job Noorman via llvm-commits]

https://github.com/mtvec created https://github.com/llvm/llvm-project/pull/69836

We used to hard-code target features for RISC-V. However, most features (with the exception of relax) are stored in the object file. This patch extracts those features to ensure BOLT's output doesn't use any features not present in the input file.

>From d5034e57ece3572aa6ba5fe58611c35a5a642792 Mon Sep 17 00:00:00 2001
From: Job Noorman <jnoorman at igalia.com>
Date: Sat, 21 Oct 2023 12:39:17 +0200
Subject: [PATCH] [BOLT][RISCV] Use target features from object file

We used to hard-code target features for RISC-V. However, most features
(with the exception of relax) are stored in the object file. This patch
extracts those features to ensure BOLT's output doesn't use any features
not present in the input file.
---
 bolt/lib/Core/BinaryContext.cpp       | 17 +++++++++++++----
 bolt/test/RISCV/call-annotations.s    |  3 ++-
 bolt/test/RISCV/internal-func-reloc.s | 18 +++++++-----------
 3 files changed, 22 insertions(+), 16 deletions(-)

diff --git a/bolt/lib/Core/BinaryContext.cpp b/bolt/lib/Core/BinaryContext.cpp
index f19460f8c1f529c..acc441aca480d49 100644
--- a/bolt/lib/Core/BinaryContext.cpp
+++ b/bolt/lib/Core/BinaryContext.cpp
@@ -118,7 +118,7 @@ Expected<std::unique_ptr<BinaryContext>>
 BinaryContext::createBinaryContext(const ObjectFile *File, bool IsPIC,
                                    std::unique_ptr<DWARFContext> DwCtx) {
   StringRef ArchName = "";
-  StringRef FeaturesStr = "";
+  std::string FeaturesStr = "";
   switch (File->getArch()) {
   case llvm::Triple::x86_64:
     ArchName = "x86-64";
@@ -128,11 +128,20 @@ BinaryContext::createBinaryContext(const ObjectFile *File, bool IsPIC,
     ArchName = "aarch64";
     FeaturesStr = "+all";
     break;
-  case llvm::Triple::riscv64:
+  case llvm::Triple::riscv64: {
     ArchName = "riscv64";
-    // RV64GC
-    FeaturesStr = "+m,+a,+f,+d,+zicsr,+zifencei,+c,+relax";
+    Expected<SubtargetFeatures> Features = File->getFeatures();
+
+    if (auto E = Features.takeError())
+      return E;
+
+    // We rely on relaxation for some transformations (e.g., promoting all calls
+    // to PseudoCALL and then making JITLink relax them). Since the relax
+    // feature is not stored in the object file, we manually enable it.
+    Features->AddFeature("relax");
+    FeaturesStr = Features->getString();
     break;
+  }
   default:
     return createStringError(std::errc::not_supported,
                              "BOLT-ERROR: Unrecognized machine in ELF file");
diff --git a/bolt/test/RISCV/call-annotations.s b/bolt/test/RISCV/call-annotations.s
index bc539bb0ec7796b..477c4693cd6dd72 100644
--- a/bolt/test/RISCV/call-annotations.s
+++ b/bolt/test/RISCV/call-annotations.s
@@ -1,12 +1,13 @@
 /// Test that annotations are properly carried over to fixed calls.
 /// Note that --enable-bat is used to force offsets to be kept.
 
-// RUN: llvm-mc -triple riscv64 -filetype obj -o %t.o %s
+// RUN: llvm-mc -triple riscv64 -mattr=+c -filetype obj -o %t.o %s
 // RUN: ld.lld --emit-relocs -o %t %t.o
 // RUN: llvm-bolt --enable-bat --print-cfg --print-fix-riscv-calls \
 // RUN:     -o /dev/null %t | FileCheck %s
 
   .text
+  .option norvc
   .global f
   .p2align 1
 f:
diff --git a/bolt/test/RISCV/internal-func-reloc.s b/bolt/test/RISCV/internal-func-reloc.s
index ea99b564fe42c15..c6c74bed92efea7 100644
--- a/bolt/test/RISCV/internal-func-reloc.s
+++ b/bolt/test/RISCV/internal-func-reloc.s
@@ -2,18 +2,14 @@
 /// get transformed by BOLT. The tests rely on the "remove-nops" optimization:
 /// if nops got removed from the function, it got transformed by BOLT.
 
-// RUN: %clang %cflags -o %t %s
+// RUN: llvm-mc -triple riscv64 -filetype=obj -o %t.o %s
+// RUN: ld.lld --emit-relocs -o %t %t.o
 // RUN: llvm-bolt -o %t.bolt %t
 // RUN: llvm-objdump -d %t.bolt | FileCheck %s
 
   .text
-
-  /// These options are only used to make the assembler output easier to predict
-  .option norelax
-  .option norvc
-
   .globl _start
-  .p2align 1
+  .p2align 2
 // CHECK: <_start>:
 // CHECK-NEXT: j 0x{{.*}} <_start>
 _start:
@@ -23,10 +19,10 @@ _start:
   .size _start, .-_start
 
   .globl f
-  .p2align 1
+  .p2align 2
 // CHECK: <f>:
-// CHECK-NEXT: auipc a0, 0
-// CHECK-NEXT: addi a0, a0, 64
+// CHECK-NEXT: auipc a0, [[#]]
+// CHECK-NEXT: addi a0, a0, [[#]]
 f:
   nop
 1:
@@ -37,7 +33,7 @@ f:
   .size f, .-f
 
   .globl g
-  .p2align 1
+  .p2align 2
 g:
   ret
   .size g, .-g