[llvm] 2e83a0e - [asan] Fixed a runtime crash.

[Kirill Stoimenov via llvm-commits]

Author: Kirill Stoimenov
Date: 2021-08-26T20:30:25Z
New Revision: 2e83a0efb9065fdc526b92cfe0f89ca53ca547d7

URL: https://github.com/llvm/llvm-project/commit/2e83a0efb9065fdc526b92cfe0f89ca53ca547d7
DIFF: https://github.com/llvm/llvm-project/commit/2e83a0efb9065fdc526b92cfe0f89ca53ca547d7.diff

LOG: [asan] Fixed a runtime crash.

Looks like the NoRegister has some effect on the final code that is generated. My guess is that some optimization kicks in at the end?

When I use -S to dump the assembly I get the correct version with 'shrq    $3, %r8':
        movq    %r9, %r8
        shrq    $3, %r8
        movsbl  2147450880(%r8), %r8d

But, when I disassemble the final binary I get RAX in stead of R8:
        mov    %r9,%r8
        shr    $0x3,%rax
        movsbl 0x7fff8000(%r8),%r8d

Reviewed By: vitalybuka

Differential Revision: https://reviews.llvm.org/D108745

Added: 
    

Modified: 
    llvm/lib/Target/X86/X86MCInstLower.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Target/X86/X86MCInstLower.cpp b/llvm/lib/Target/X86/X86MCInstLower.cpp
index c7740113f89e2..e827afef848bd 100644
--- a/llvm/lib/Target/X86/X86MCInstLower.cpp
+++ b/llvm/lib/Target/X86/X86MCInstLower.cpp
@@ -1370,12 +1370,12 @@ void X86AsmPrinter::emitAsanMemaccessPartial(Module &M, unsigned Reg,
       STI);
   OutStreamer->emitInstruction(MCInstBuilder(X86::SHR64ri)
                                    .addReg(X86::R8)
-                                   .addReg(X86::NoRegister)
+                                   .addReg(X86::R8)
                                    .addImm(MappingScale),
                                STI);
   if (OrShadowOffset) {
     OutStreamer->emitInstruction(MCInstBuilder(X86::OR64ri32)
-                                     .addReg(X86::NoRegister)
+                                     .addReg(X86::R8)
                                      .addReg(X86::R8)
                                      .addImm(ShadowBase),
                                  STI);