[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

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.

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() { }

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;
 }

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(

llvm/test/MC/AArch64/expr-shr.s

@@ -0,0 +1,8 @@
+// RUN: llvm-mc -triple aarch64-unknown-unknown-elf %s | FileCheck %s --check-prefix=ELF
+// RUN: llvm-mc -triple aarch64-unknown-darwin %s | FileCheck %s --check-prefix=DARWIN
+
+.data
+
+// ELF: .xword 3
+// DARWIN: .quad 3
+.quad (~0 >> 62)

llvm/test/MC/ARM/bracket-exprs.s

@@ -1,7 +1,7 @@
 // RUN: llvm-mc -triple arm-unknown-linux %s | FileCheck %s
 
 // CHECK: .byte 1
-.if [~0 >> 1] == -1
+.if [~0 >> 63] == 1
 .byte 1
 .else
 .byte 2

llvm/test/MC/AsmParser/expr-shr.s

@@ -0,0 +1,13 @@
+// RUN: llvm-mc -triple x86_64-unknown-unknown-elf %s | FileCheck %s --check-prefix=CHECK
+// RUN: llvm-mc -triple x86_64-pc-windows-msvc %s | FileCheck %s --check-prefix=MSVC
+// RUN: llvm-mc -triple x86_64-unknown-darwin %s | FileCheck %s --check-prefix=DARWIN
+
+.data
+
+// CHECK: .quad 3
+
+// Both COFF and Darwin still use AShr.
+// MSVC: .quad -1
+// DARWIN: .quad -1
+
+.quad (~0 >> 62)

llvm/test/MC/ELF/bracket-exprs.s

@@ -1,7 +1,7 @@
 // RUN: llvm-mc -triple i386-unknown-unknown %s | FileCheck %s
 
 // CHECK: .byte 1
-.if [~0 >> 1] == -1
+.if [~0 >> 63] == 1
 .byte 1
 .else
 .byte 2