[mips] Add comment which explains why we need to change the assembler options before...

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225521 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Target/Mips/MipsAsmPrinter.cpp b/lib/Target/Mips/MipsAsmPrinter.cpp
index 53b79eeacea69f7c0e60b8bc2471dd215f1643fc..50c0441e0dd474aa123667a27deed90107aa0308 100644 (file)
--- a/lib/Target/Mips/MipsAsmPrinter.cpp
+++ b/lib/Target/Mips/MipsAsmPrinter.cpp
@@ -747,6 +747,12 @@ void MipsAsmPrinter::emitInlineAsmStart(
     const MCSubtargetInfo &StartInfo) const {
   MipsTargetStreamer &TS = getTargetStreamer();
 
+  // GCC's choice of assembler options for inline assembly code ('at', 'macro'
+  // and 'reorder') is different from LLVM's choice for generated code ('noat',
+  // 'nomacro' and 'noreorder').
+  // In order to maintain compatibility with inline assembly code which depends
+  // on GCC's assembler options being used, we have to switch to those options
+  // for the duration of the inline assembly block and then switch back.
   TS.emitDirectiveSetPush();
   TS.emitDirectiveSetAt();
   TS.emitDirectiveSetMacro();