From af1b48bfdcc4cf1602dca45fe2511a426f48879e Mon Sep 17 00:00:00 2001 From: Sanjay Patel Date: Tue, 10 Nov 2015 19:24:31 +0000 Subject: [ARM] add overrides for isCheapToSpeculateCttz() and isCheapToSpeculateCtlz() ARM V6T2 has instructions for efficient count-leading/trailing-zeros, so this should be considered a cheap operation (and therefore fair game for speculation) for any ARM V6T2 implementation. The net result of allowing this speculation for the regression tests in this patch is that we get this code: ctlz: clz r0, r0 bx lr cttz: rbit r0, r0 clz r0, r0 bx lr Instead of: ctlz: cmp r0, #0 moveq r0, #32 clzne r0, r0 bx lr cttz: cmp r0, #0 moveq r0, #32 rbitne r0, r0 clzne r0, r0 bx lr This will help solve a general speculation/despeculation problem noted in PR24818: https://llvm.org/bugs/show_bug.cgi?id=24818 Differential Revision: http://reviews.llvm.org/D14469 llvm-svn: 252639 --- llvm/lib/Target/ARM/ARMISelLowering.cpp | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'llvm/lib/Target/ARM/ARMISelLowering.cpp') diff --git a/llvm/lib/Target/ARM/ARMISelLowering.cpp b/llvm/lib/Target/ARM/ARMISelLowering.cpp index b83d3f78a34..01c8d7534ee 100644 --- a/llvm/lib/Target/ARM/ARMISelLowering.cpp +++ b/llvm/lib/Target/ARM/ARMISelLowering.cpp @@ -11841,6 +11841,14 @@ bool ARMTargetLowering::canCombineStoreAndExtract(Type *VectorTy, Value *Idx, return false; } +bool ARMTargetLowering::isCheapToSpeculateCttz() const { + return Subtarget->hasV6T2Ops(); +} + +bool ARMTargetLowering::isCheapToSpeculateCtlz() const { + return Subtarget->hasV6T2Ops(); +} + Value *ARMTargetLowering::emitLoadLinked(IRBuilder<> &Builder, Value *Addr, AtomicOrdering Ord) const { Module *M = Builder.GetInsertBlock()->getParent()->getParent(); -- cgit v1.2.3