[PATCH] D45773: [RISCV] Don't fold symbol diff

[Edward Jones via Phabricator via llvm-commits]

edward-jones updated this revision to Diff 146558.

https://reviews.llvm.org/D45773

Files:
  include/llvm/MC/MCObjectStreamer.h
  lib/MC/MCObjectStreamer.cpp
  test/CodeGen/RISCV/fixups-diff.ll


Index: test/CodeGen/RISCV/fixups-diff.ll
===================================================================
--- /dev/null
+++ test/CodeGen/RISCV/fixups-diff.ll
@@ -0,0 +1,46 @@
+; RUN: llc -filetype=obj -mtriple=riscv32 -mattr=+relax %s -o - \
+; RUN:     | llvm-readobj -r | FileCheck -check-prefix=RELAX %s
+; RUN: llc -filetype=obj -mtriple=riscv32 -mattr=-relax %s -o - \
+; RUN:     | llvm-readobj -r | FileCheck -check-prefix=NORELAX %s
+
+; Check that a difference between two symbols in the same fragment
+; causes relocations to be emitted if and only if relaxation is enabled.
+;
+; This specific test is checking that the size of the function in
+; the debug information is represented by a relocation. This isn't
+; an assembly test as the assembler takes a different path through
+; LLVM, which is already covered by the fixups-expr.s test.
+
+source_filename = "tmp.c"
+target datalayout = "e-m:e-p:32:32-i64:64-n32-S128"
+target triple = "riscv32"
+
+define i32 @main() !dbg !7 {
+entry:
+  %retval = alloca i32, align 4
+  store i32 0, i32* %retval, align 4
+  ret i32 0
+}
+
+; RELAX: 0x22 R_RISCV_ADD32 - 0x0
+; RELAX: 0x22 R_RISCV_SUB32 - 0x0
+; RELAX: 0x2B R_RISCV_ADD32 - 0x0
+; RELAX: 0x2B R_RISCV_SUB32 - 0x0
+; NORELAX-NOT: R_RISCV_ADD32
+
+!llvm.dbg.cu = !{!0}
+!llvm.module.flags = !{!3, !4, !5}
+!llvm.ident = !{!6}
+
+!0 = distinct !DICompileUnit(language: DW_LANG_C99, file: !1, producer: "clang", isOptimized: false, runtimeVersion: 0, emissionKind: FullDebug, enums: !2)
+!1 = !DIFile(filename: "fixups-diff.ll", directory: "test/MC/RISCV")
+!2 = !{}
+!3 = !{i32 2, !"Dwarf Version", i32 4}
+!4 = !{i32 2, !"Debug Info Version", i32 3}
+!5 = !{i32 1, !"wchar_size", i32 4}
+!6 = !{!"clang"}
+!7 = distinct !DISubprogram(name: "main", scope: !1, file: !1, line: 1, type: !8, isLocal: false, isDefinition: true, scopeLine: 1, flags: DIFlagPrototyped, isOptimized: false, unit: !0)
+!8 = !DISubroutineType(types: !9)
+!9 = !{!10}
+!10 = !DIBasicType(name: "int", size: 32, encoding: DW_ATE_signed)
+!11 = !DILocation(line: 2, column: 3, scope: !7)
Index: lib/MC/MCObjectStreamer.cpp
===================================================================
--- lib/MC/MCObjectStreamer.cpp
+++ lib/MC/MCObjectStreamer.cpp
@@ -88,9 +88,12 @@
 
 // As a compile-time optimization, avoid allocating and evaluating an MCExpr
 // tree for (Hi - Lo) when Hi and Lo are offsets into the same fragment.
-static Optional<uint64_t> absoluteSymbolDiff(const MCSymbol *Hi,
-                                             const MCSymbol *Lo) {
+Optional<uint64_t>
+MCObjectStreamer::absoluteSymbolDiff(const MCSymbol *Hi, const MCSymbol *Lo) {
   assert(Hi && Lo);
+  if (getAssembler().getBackendPtr()->requiresDiffExpressionRelocations())
+    return None;
+
   if (!Hi->getFragment() || Hi->getFragment() != Lo->getFragment() ||
       Hi->isVariable() || Lo->isVariable())
     return None;
Index: include/llvm/MC/MCObjectStreamer.h
===================================================================
--- include/llvm/MC/MCObjectStreamer.h
+++ include/llvm/MC/MCObjectStreamer.h
@@ -168,11 +168,18 @@
 
   void FinishImpl() override;
 
+private:
+  Optional<uint64_t> absoluteSymbolDiff(const MCSymbol *hi,
+                                        const MCSymbol *Lo);
+
+public:
   /// Emit the absolute difference between two symbols if possible.
   ///
   /// Emit the absolute difference between \c Hi and \c Lo, as long as we can
   /// compute it.  Currently, that requires that both symbols are in the same
-  /// data fragment.  Otherwise, do nothing and return \c false.
+  /// data fragment and that the target has not specified that diff expressions
+  /// require relocations to be emitted. Otherwise, do nothing and return
+  /// \c false.
   ///
   /// \pre Offset of \c Hi is greater than the offset \c Lo.
   void emitAbsoluteSymbolDiff(const MCSymbol *Hi, const MCSymbol *Lo,


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