Andrea Di Biagio 70a7cda495 [CodeGenPrepare] Teach when it is profitable to speculate calls to @llvm.cttz/ctlz. ... If the control flow is modelling an if-statement where the only instruction in the 'then' basic block (excluding the terminator) is a call to cttz/ctlz, CodeGenPrepare can try to speculate the cttz/ctlz call and simplify the control flow graph. Example: \code entry: %cmp = icmp eq i64 %val, 0 br i1 %cmp, label %end.bb, label %then.bb then.bb: %c = tail call i64 @llvm.cttz.i64(i64 %val, i1 true) br label %end.bb end.bb: %cond = phi i64 [ %c, %then.bb ], [ 64, %entry] \code In this example, basic block %then.bb is taken if value %val is not zero. Also, the phi node in %end.bb would propagate the size-of in bits of %val only if %val is equal to zero. With this patch, CodeGenPrepare will try to hoist the call to cttz from %then.bb into basic block %entry only if cttz is cheap to speculate for the target. Added two new hooks in TargetLowering.h to let targets customize the behavior (i.e. decide whether it is cheap or not to speculate calls to cttz/ctlz). The two new methods are 'isCheapToSpeculateCtlz' and 'isCheapToSpeculateCttz'. By default, both methods return 'false'. On X86, method 'isCheapToSpeculateCtlz' returns true only if the target has LZCNT. Method 'isCheapToSpeculateCttz' only returns true if the target has BMI. Differential Revision: http://reviews.llvm.org/D6728 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@224899 91177308-0d34-0410-b5e6-96231b3b80d8		2014-12-28 11:07:35 +00:00
..
Analysis	ValueTracking: Small cleanup in ComputeNumSignBits	2014-12-26 09:20:17 +00:00
AsmParser	IR: Make metadata typeless in assembly	2014-12-15 19:07:53 +00:00
Bitcode	Fix Visual C++ error "'llvm::make_unique' : ambiguous call to overloaded function".	2014-12-18 10:03:35 +00:00
CodeGen	[CodeGenPrepare] Teach when it is profitable to speculate calls to @llvm.cttz/ctlz.	2014-12-28 11:07:35 +00:00
DebugInfo	[DebugInfo] Move all DWARF headers to the public include directory.	2014-12-19 18:26:33 +00:00
ExecutionEngine	[C API] Expose LLVMGetGlobalValueAddress and LLVMGetFunctionAddress.	2014-12-22 18:53:11 +00:00
IR	Masked Load/Store - Changed the order of parameters in intrinsics.	2014-12-25 07:49:20 +00:00
IRReader	Remove unused variable. NFC.	2014-11-06 23:16:57 +00:00
LineEditor
Linker	Finish removing DestroySource.	2014-12-23 19:16:45 +00:00
LTO	LTO: Lazy-load LTOModule in local contexts	2014-12-17 22:05:42 +00:00
MC	MC: Label definitions are permitted after .set directives	2014-12-24 10:27:50 +00:00
Object	Add printing the LC_THREAD load commands with llvm-objdump’s -private-headers.	2014-12-23 22:56:39 +00:00
Option	Add an overload of getLastArgNoClaim taking two OptSpecifiers.	2014-09-12 19:42:53 +00:00
ProfileData	llvm-cov: Sink some reporting logic into CoverageMapping	2014-11-14 01:50:32 +00:00
Support	Add missing implementation of 'sys::path::is_other' to the support library.	2014-12-18 18:19:47 +00:00
TableGen	Clean up static analyzer warnings.	2014-12-12 21:48:03 +00:00
Target	[CodeGenPrepare] Teach when it is profitable to speculate calls to @llvm.cttz/ctlz.	2014-12-28 11:07:35 +00:00
Transforms	InstCombine: Infer nuw for multiplies	2014-12-26 09:50:35 +00:00
CMakeLists.txt
LLVMBuild.txt
Makefile