Previously we used a select and the zero_undef=true intrinsic. In -O2 this pattern will get optimized to zero_undef=false. But in -O0 this optimization won't happen. This results in a compare and cmov being wrapped around a tzcnt/lzcnt instruction.
By using the zero_undef=false intrinsic directly without the select, we can improve the -O0 codegen to just an lzcnt/tzcnt instruction.
Differential Revision: https://reviews.llvm.org/D52392
llvm-svn: 343126
The X86 clang/test/CodeGen/*builtins.c tests define the mm_malloc.h include
guard as a hack for avoiding its inclusion (mm_malloc.h requires a hosted
environment since it expects stdlib.h to be available - which is not the case
in these internal clang codegen tests).
This patch removes this hack and instead passes -ffreestanding to clang cc1.
Differential Revision: https://reviews.llvm.org/D24825
llvm-svn: 282581
Craig Topper