[PATCH] D48069: [cmake] Disable a GCC optimization when building LLVM for MIPS

[Simon Dardis via Phabricator via llvm-commits]

sdardis created this revision.
sdardis added a reviewer: beanz.
Herald added subscribers: atanasyan, arichardson, mgorny.

GCC when compiling LLVM for MIPS can introduce a jump to an uninitialized value
when shrink wrapping is enabled. As shrink wrapping is enabled in GCC at all 
optimization levels, it must be disabled. This bug exists for all versions of
GCC since 4.9.2.

This partially resolves PR37701 / GCC PR target/86069.


Repository:
  rL LLVM

https://reviews.llvm.org/D48069

Files:
  cmake/modules/HandleLLVMOptions.cmake


Index: cmake/modules/HandleLLVMOptions.cmake
===================================================================
--- cmake/modules/HandleLLVMOptions.cmake
+++ cmake/modules/HandleLLVMOptions.cmake
@@ -223,6 +223,11 @@
   else()
     add_flag_or_print_warning("-fPIC" FPIC)
   endif()
+  # GCC for MIPS can miscompile LLVM due to PR37701.
+  if(CMAKE_COMPILER_IS_GNUCXX AND LLVM_NATIVE_ARCH STREQUAL "Mips" AND
+         NOT Uppercase_CMAKE_BUILD_TYPE STREQUAL "DEBUG")
+    add_flag_or_print_warning("-fno-shrink-wrap" FNO_SHRINK_WRAP)
+  endif()
 endif()
 
 if(NOT WIN32 AND NOT CYGWIN)


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