Compute A-B when A or B is weak.

Similar to r235222, but for the weak symbol case.

In an "ideal" assembler/object format an expression would always refer to the
final value and A-B would only be computed from a section in the same
comdat as A and B with A and B strong.

Unfortunately that is not the case with debug info on ELF, so we need an
heuristic.  Since we need an heuristic, we may as well use the same one as
gas:

* call weak_sym : produces a relocation, even if in the same section.
* A - weak_sym and weak_sym -A: don't produce a relocation if we can
  compute it.

This fixes pr23272 and changes the fix of pr22815 to match what gas does.

llvm-svn: 235227

diff --git a/llvm/include/llvm/MC/MCMachObjectWriter.h b/llvm/include/llvm/MC/MCMachObjectWriter.h
index a06f44a..7feeec3 100644 (file)
--- a/llvm/include/llvm/MC/MCMachObjectWriter.h
+++ b/llvm/include/llvm/MC/MCMachObjectWriter.h
@@ -264,7 +264,6 @@ public:
 
   bool IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
                                               const MCSymbolData &DataA,
-                                              const MCSymbolData *DataB,
                                               const MCFragment &FB,
                                               bool InSet,
                                               bool IsPCRel) const override;

diff --git a/llvm/include/llvm/MC/MCObjectWriter.h b/llvm/include/llvm/MC/MCObjectWriter.h
index f8e2821..b490e92 100644 (file)
--- a/llvm/include/llvm/MC/MCObjectWriter.h
+++ b/llvm/include/llvm/MC/MCObjectWriter.h
@@ -94,7 +94,6 @@ public:
 
   virtual bool IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
                                                       const MCSymbolData &DataA,
-                                                      const MCSymbolData *DataB,
                                                       const MCFragment &FB,
                                                       bool InSet,
                                                       bool IsPCRel) const;

diff --git a/llvm/lib/MC/ELFObjectWriter.cpp b/llvm/lib/MC/ELFObjectWriter.cpp
index 32ec969..1646fe5 100644 (file)
--- a/llvm/lib/MC/ELFObjectWriter.cpp
+++ b/llvm/lib/MC/ELFObjectWriter.cpp
@@ -275,7 +275,6 @@ class ELFObjectWriter : public MCObjectWriter {
     bool
     IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
                                            const MCSymbolData &DataA,
-                                           const MCSymbolData *DataB,
                                            const MCFragment &FB,
                                            bool InSet,
                                            bool IsPCRel) const override;
@@ -1669,13 +1668,15 @@ void ELFObjectWriter::WriteObject(MCAssembler &Asm,
 }
 
 bool ELFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
-    const MCAssembler &Asm, const MCSymbolData &DataA,
-    const MCSymbolData *DataB, const MCFragment &FB, bool InSet,
-    bool IsPCRel) const {
-  if (!InSet && (::isWeak(DataA) || (DataB && ::isWeak(*DataB))))
-    return false;
-  return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
-      Asm, DataA, DataB, FB, InSet, IsPCRel);
+    const MCAssembler &Asm, const MCSymbolData &DataA, const MCFragment &FB,
+    bool InSet, bool IsPCRel) const {
+  if (IsPCRel) {
+    assert(!InSet);
+    if (::isWeak(DataA))
+      return false;
+  }
+  return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(Asm, DataA, FB,
+                                                                InSet, IsPCRel);
 }
 
 bool ELFObjectWriter::isWeak(const MCSymbolData &SD) const {

diff --git a/llvm/lib/MC/MCAssembler.cpp b/llvm/lib/MC/MCAssembler.cpp
index d09e383..a7df95a 100644 (file)
--- a/llvm/lib/MC/MCAssembler.cpp
+++ b/llvm/lib/MC/MCAssembler.cpp
@@ -504,7 +504,7 @@ bool MCAssembler::evaluateFixup(const MCAsmLayout &Layout,
       } else {
         const MCSymbolData &DataA = getSymbolData(SA);
         IsResolved = getWriter().IsSymbolRefDifferenceFullyResolvedImpl(
-            *this, DataA, nullptr, *DF, false, true);
+            *this, DataA, *DF, false, true);
       }
     }
   } else {

diff --git a/llvm/lib/MC/MCObjectWriter.cpp b/llvm/lib/MC/MCObjectWriter.cpp
index e40c07d..e90dea8 100644 (file)
--- a/llvm/lib/MC/MCObjectWriter.cpp
+++ b/llvm/lib/MC/MCObjectWriter.cpp
@@ -36,13 +36,12 @@ bool MCObjectWriter::IsSymbolRefDifferenceFullyResolved(
     return false;
 
   return IsSymbolRefDifferenceFullyResolvedImpl(
-      Asm, DataA, &DataB, *DataB.getFragment(), InSet, false);
+      Asm, DataA, *DataB.getFragment(), InSet, false);
 }
 
 bool MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
-    const MCAssembler &Asm, const MCSymbolData &DataA,
-    const MCSymbolData *DataB, const MCFragment &FB, bool InSet,
-    bool IsPCRel) const {
+    const MCAssembler &Asm, const MCSymbolData &DataA, const MCFragment &FB,
+    bool InSet, bool IsPCRel) const {
   const MCSection &SecA = DataA.getSymbol().getSection();
   const MCSection &SecB = FB.getParent()->getSection();
   // On ELF and COFF  A - B is absolute if A and B are in the same section.

diff --git a/llvm/lib/MC/MachObjectWriter.cpp b/llvm/lib/MC/MachObjectWriter.cpp
index 97143a9..dc68a89 100644 (file)
--- a/llvm/lib/MC/MachObjectWriter.cpp
+++ b/llvm/lib/MC/MachObjectWriter.cpp
@@ -669,13 +669,9 @@ void MachObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
   BindIndirectSymbols(Asm);
 }
 
-bool MachObjectWriter::
-IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
-                                       const MCSymbolData &DataA,
-                                       const MCSymbolData *DataB,
-                                       const MCFragment &FB,
-                                       bool InSet,
-                                       bool IsPCRel) const {
+bool MachObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
+    const MCAssembler &Asm, const MCSymbolData &DataA, const MCFragment &FB,
+    bool InSet, bool IsPCRel) const {
   if (InSet)
     return true;
 

diff --git a/llvm/lib/MC/WinCOFFObjectWriter.cpp b/llvm/lib/MC/WinCOFFObjectWriter.cpp
index a4b6bf9..5854630 100644 (file)
--- a/llvm/lib/MC/WinCOFFObjectWriter.cpp
+++ b/llvm/lib/MC/WinCOFFObjectWriter.cpp
@@ -172,7 +172,6 @@ public:
 
   bool IsSymbolRefDifferenceFullyResolvedImpl(const MCAssembler &Asm,
                                               const MCSymbolData &DataA,
-                                              const MCSymbolData *DataB,
                                               const MCFragment &FB, bool InSet,
                                               bool IsPCRel) const override;
 
@@ -649,17 +648,16 @@ void WinCOFFObjectWriter::ExecutePostLayoutBinding(MCAssembler &Asm,
 }
 
 bool WinCOFFObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
-    const MCAssembler &Asm, const MCSymbolData &DataA,
-    const MCSymbolData *DataB, const MCFragment &FB, bool InSet,
-    bool IsPCRel) const {
+    const MCAssembler &Asm, const MCSymbolData &DataA, const MCFragment &FB,
+    bool InSet, bool IsPCRel) const {
   // MS LINK expects to be able to replace all references to a function with a
   // thunk to implement their /INCREMENTAL feature.  Make sure we don't optimize
   // away any relocations to functions.
   if ((((DataA.getFlags() & COFF::SF_TypeMask) >> COFF::SF_TypeShift) >>
        COFF::SCT_COMPLEX_TYPE_SHIFT) == COFF::IMAGE_SYM_DTYPE_FUNCTION)
     return false;
-  return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(
-      Asm, DataA, DataB, FB, InSet, IsPCRel);
+  return MCObjectWriter::IsSymbolRefDifferenceFullyResolvedImpl(Asm, DataA, FB,
+                                                                InSet, IsPCRel);
 }
 
 bool WinCOFFObjectWriter::isWeak(const MCSymbolData &SD) const {

diff --git a/llvm/test/MC/ELF/weak-diff.s b/llvm/test/MC/ELF/weak-diff.s
index d270bbb..ded89b8 100644 (file)
--- a/llvm/test/MC/ELF/weak-diff.s
+++ b/llvm/test/MC/ELF/weak-diff.s
@@ -1,6 +1,10 @@
-// RUN: not llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu %s -o %t 2>&1 | FileCheck %s
+// RUN: llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu < %s | llvm-readobj -r | FileCheck %s
 
-// CHECK: error: Cannot represent a subtraction with a weak symbol
+// CHECK:      Relocations [
+// CHECK-NEXT:   Section ({{.*}}) .rela.text {
+// CHECK-NEXT:     0x1D R_X86_64_PC32 f2 0xFFFFFFFFFFFFFFFC
+// CHECK-NEXT:   }
+// CHECK-NEXT: ]
 
 .weak f
 .weak g
@@ -10,3 +14,13 @@ g:
     nop
 
 .quad g - f
+
+
+.weak f2
+f2:
+    nop
+g2:
+    nop
+.quad g2 - f2
+.quad f2 - g2
+call f2

diff --git a/llvm/test/MC/ELF/weak-diff2.s b/llvm/test/MC/ELF/weak-diff2.s
deleted file mode 100644 (file)
index daf64a4..0000000
--- a/llvm/test/MC/ELF/weak-diff2.s
+++ /dev/null
@@ -1,10 +0,0 @@
-// RUN: not llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu %s -o %t 2>&1 | FileCheck %s
-
-// CHECK: error: Cannot represent a subtraction with a weak symbol
-
-.weak f
-f:
-    nop
-g:
-    nop
-.quad g - f