[llvm] r339864 - [RISCV][MC] Don't fold symbol differences if requiresDiffExpressionRelocations is true
Alex Bradbury via llvm-commits
llvm-commits at lists.llvm.org
Thu Aug 16 04:26:38 PDT 2018
Author: asb
Date: Thu Aug 16 04:26:37 2018
New Revision: 339864
URL: http://llvm.org/viewvc/llvm-project?rev=339864&view=rev
Log:
[RISCV][MC] Don't fold symbol differences if requiresDiffExpressionRelocations is true
When emitting the difference between two symbols, the standard behavior is
that the difference will be resolved to an absolute value if both of the
symbols are offsets from the same data fragment. This is undesirable on
architectures such as RISC-V where relaxation in the linker may cause the
computed difference to become invalid. This caused an issue when compiling to
object code, where the size of a function in the debug information was already
calculated even though it could change as a consequence of relaxation in the
subsequent linking stage.
This patch inhibits the resolution of symbol differences to absolute values
where the target's AsmBackend has declared that it does not want these to be
folded.
Differential Revision: https://reviews.llvm.org/D45773
Patch by Edward Jones.
Added:
llvm/trunk/test/CodeGen/RISCV/fixups-diff.ll
Modified:
llvm/trunk/include/llvm/MC/MCObjectStreamer.h
llvm/trunk/lib/MC/MCObjectStreamer.cpp
Modified: llvm/trunk/include/llvm/MC/MCObjectStreamer.h
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/include/llvm/MC/MCObjectStreamer.h?rev=339864&r1=339863&r2=339864&view=diff
==============================================================================
--- llvm/trunk/include/llvm/MC/MCObjectStreamer.h (original)
+++ llvm/trunk/include/llvm/MC/MCObjectStreamer.h Thu Aug 16 04:26:37 2018
@@ -179,7 +179,9 @@ public:
///
/// 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,
Modified: llvm/trunk/lib/MC/MCObjectStreamer.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/MC/MCObjectStreamer.cpp?rev=339864&r1=339863&r2=339864&view=diff
==============================================================================
--- llvm/trunk/lib/MC/MCObjectStreamer.cpp (original)
+++ llvm/trunk/lib/MC/MCObjectStreamer.cpp Thu Aug 16 04:26:37 2018
@@ -61,9 +61,12 @@ void MCObjectStreamer::flushPendingLabel
// 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) {
+static Optional<uint64_t>
+absoluteSymbolDiff(MCAssembler &Asm, const MCSymbol *Hi, const MCSymbol *Lo) {
assert(Hi && Lo);
+ if (Asm.getBackendPtr()->requiresDiffExpressionRelocations())
+ return None;
+
if (!Hi->getFragment() || Hi->getFragment() != Lo->getFragment() ||
Hi->isVariable() || Lo->isVariable())
return None;
@@ -74,7 +77,7 @@ static Optional<uint64_t> absoluteSymbol
void MCObjectStreamer::emitAbsoluteSymbolDiff(const MCSymbol *Hi,
const MCSymbol *Lo,
unsigned Size) {
- if (Optional<uint64_t> Diff = absoluteSymbolDiff(Hi, Lo)) {
+ if (Optional<uint64_t> Diff = absoluteSymbolDiff(getAssembler(), Hi, Lo)) {
EmitIntValue(*Diff, Size);
return;
}
@@ -83,7 +86,7 @@ void MCObjectStreamer::emitAbsoluteSymbo
void MCObjectStreamer::emitAbsoluteSymbolDiffAsULEB128(const MCSymbol *Hi,
const MCSymbol *Lo) {
- if (Optional<uint64_t> Diff = absoluteSymbolDiff(Hi, Lo)) {
+ if (Optional<uint64_t> Diff = absoluteSymbolDiff(getAssembler(), Hi, Lo)) {
EmitULEB128IntValue(*Diff);
return;
}
Added: llvm/trunk/test/CodeGen/RISCV/fixups-diff.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/RISCV/fixups-diff.ll?rev=339864&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/RISCV/fixups-diff.ll (added)
+++ llvm/trunk/test/CodeGen/RISCV/fixups-diff.ll Thu Aug 16 04:26:37 2018
@@ -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)
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