[llvm] 0ca426d - [llvm-mca] Improve barriers for strict region marking (PR52198)

[Simon Pilgrim via llvm-commits]

Author: Simon Pilgrim
Date: 2022-01-21T11:25:05Z
New Revision: 0ca426d6ac65b84c70ac7fd9511628ce5115423e

URL: https://github.com/llvm/llvm-project/commit/0ca426d6ac65b84c70ac7fd9511628ce5115423e
DIFF: https://github.com/llvm/llvm-project/commit/0ca426d6ac65b84c70ac7fd9511628ce5115423e.diff

LOG: [llvm-mca] Improve barriers for strict region marking (PR52198)

As suggested on the bug, to help (but not completely....) stop folded instructions crossing the inline asm barriers used for llvm-mca analysis, we should recommend tagging with memory captures/attributes.

Differential Revision: https://reviews.llvm.org/D117788

Added: 
    

Modified: 
    llvm/docs/CommandGuide/llvm-mca.rst

Removed: 
    


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diff  --git a/llvm/docs/CommandGuide/llvm-mca.rst b/llvm/docs/CommandGuide/llvm-mca.rst
index b08f088762799..fdb45783ea663 100644
--- a/llvm/docs/CommandGuide/llvm-mca.rst
+++ b/llvm/docs/CommandGuide/llvm-mca.rst
@@ -299,9 +299,9 @@ C++. As a workaround, inline assembly directives may be used:
 .. code-block:: c++
 
   int foo(int a, int b) {
-    __asm volatile("# LLVM-MCA-BEGIN foo");
+    __asm volatile("# LLVM-MCA-BEGIN foo":::"memory");
     a += 42;
-    __asm volatile("# LLVM-MCA-END");
+    __asm volatile("# LLVM-MCA-END":::"memory");
     a *= b;
     return a;
   }