make reciprocal estimate code generation more flexible by adding command-line options (3rd try)
The first try (r238051) to land this was reverted due to ExecutionEngine build failure;
that was hopefully addressed by r238788.
The second try (r238842) to land this was reverted due to BUILD_SHARED_LIBS failure;
that was hopefully addressed by r238953.
This patch adds a TargetRecip class for processing many recip codegen possibilities.
The class is intended to handle both command-line options to llc as well
as options passed in from a front-end such as clang with the -mrecip option.
The x86 backend is updated to use the new functionality.
Only -mcpu=btver2 with -ffast-math should see a functional change from this patch.
All other x86 CPUs continue to *not* use reciprocal estimates by default with -ffast-math.
Differential Revision: http://reviews.llvm.org/D8982
llvm-svn: 239001
diff --git a/llvm/lib/Target/X86/X86TargetMachine.cpp b/llvm/lib/Target/X86/X86TargetMachine.cpp
index 4116cef..646cff7 100644
--- a/llvm/lib/Target/X86/X86TargetMachine.cpp
+++ b/llvm/lib/Target/X86/X86TargetMachine.cpp
@@ -105,6 +105,13 @@
if (Subtarget.isTargetWin64())
this->Options.TrapUnreachable = true;
+ // TODO: By default, all reciprocal estimate operations are off because
+ // that matches the behavior before TargetRecip was added (except for btver2
+ // which used subtarget features to enable this type of codegen).
+ // We should change this to match GCC behavior where everything but
+ // scalar division estimates are turned on by default with -ffast-math.
+ this->Options.Reciprocals.setDefaults("all", false, 1);
+
initAsmInfo();
}