[MC] Use LShr for constant evaluation of ">>" on ELF/arm64--darwin.

This matches other assemblers and is less unexpected (e.g. PR23227).
On ELF, I tried binutils gas v2.24 and nasm 2.10.09, and they both
agree on LShr.  On COFF, I couldn't get my hands on an assembler yet,
so don't change the behavior.  For now, don't change it on non-AArch64
Darwin either, as the other assembler is gas v1.38, which does an AShr.

llvm-svn: 235963

4 files changed, 14 insertions, 1 deletions

diff --git a/llvm/lib/MC/MCAsmInfo.cpp b/llvm/lib/MC/MCAsmInfo.cpp
index 22de8bd13dc..1a45b5a389f 100644
--- a/llvm/lib/MC/MCAsmInfo.cpp
+++ b/llvm/lib/MC/MCAsmInfo.cpp
@@ -90,7 +90,7 @@ MCAsmInfo::MCAsmInfo() {
   DwarfRegNumForCFI = false;
   NeedsDwarfSectionOffsetDirective = false;
   UseParensForSymbolVariant = false;
-  UseLogicalShr = false;
+  UseLogicalShr = true;
 
   // FIXME: Clang's logic should be synced with the logic used to initialize
   //        this member and the two implementations should be merged.
diff --git a/llvm/lib/MC/MCAsmInfoCOFF.cpp b/llvm/lib/MC/MCAsmInfoCOFF.cpp
index bb3f0d3a429..97fc76a9adb 100644
--- a/llvm/lib/MC/MCAsmInfoCOFF.cpp
+++ b/llvm/lib/MC/MCAsmInfoCOFF.cpp
@@ -36,6 +36,10 @@ MCAsmInfoCOFF::MCAsmInfoCOFF() {
   NeedsDwarfSectionOffsetDirective = true;
 
   UseIntegratedAssembler = true;
+
+  // FIXME: For now keep the previous behavior, AShr. Need to double-check
+  // other COFF-targeting assemblers and change this if necessary.
+  UseLogicalShr = false;
 }
 
 void MCAsmInfoMicrosoft::anchor() { }
diff --git a/llvm/lib/MC/MCAsmInfoDarwin.cpp b/llvm/lib/MC/MCAsmInfoDarwin.cpp
index ae9486d3db4..bb90ff2c350 100644
--- a/llvm/lib/MC/MCAsmInfoDarwin.cpp
+++ b/llvm/lib/MC/MCAsmInfoDarwin.cpp
@@ -93,4 +93,9 @@ MCAsmInfoDarwin::MCAsmInfoDarwin() {
 
   UseIntegratedAssembler = true;
   SetDirectiveSuppressesReloc = true;
+
+  // FIXME: For now keep the previous behavior, AShr, matching the previous
+  // behavior of as(1) (both -q and -Q: resp. LLVM and gas v1.38).
+  // If/when this changes, the AArch64 Darwin special case can go away.
+  UseLogicalShr = false;
 }
diff --git a/llvm/lib/Target/AArch64/MCTargetDesc/AArch64MCAsmInfo.cpp b/llvm/lib/Target/AArch64/MCTargetDesc/AArch64MCAsmInfo.cpp
index f048474fd4a..c4122040041 100644
--- a/llvm/lib/Target/AArch64/MCTargetDesc/AArch64MCAsmInfo.cpp
+++ b/llvm/lib/Target/AArch64/MCTargetDesc/AArch64MCAsmInfo.cpp
@@ -48,6 +48,10 @@ AArch64MCAsmInfoDarwin::AArch64MCAsmInfoDarwin() {
   UseDataRegionDirectives = true;
 
   ExceptionsType = ExceptionHandling::DwarfCFI;
+
+  // AArch64 Darwin doesn't have the baggage of X86/ARM, so it's fine to use
+  // LShr instead of AShr.
+  UseLogicalShr = true;
 }
 
 const MCExpr *AArch64MCAsmInfoDarwin::getExprForPersonalitySymbol(