This patch implements optimization as mentioned in PR19753: Optimize comparisons with "ashr/lshr exact" of a constanst.
It handles the errors which were seen in PR19958 where wrong code was being emitted due to earlier patch.
Added code for lshr as well as non-exact right shifts.
It implements :
(icmp eq/ne (ashr/lshr const2, A), const1)" ->
(icmp eq/ne A, Log2(const2/const1)) ->
(icmp eq/ne A, Log2(const2) - Log2(const1))
Differential Revision: http://reviews.llvm.org/D4068
llvm-svn: 213678
diff --git a/llvm/lib/Transforms/InstCombine/InstCombine.h b/llvm/lib/Transforms/InstCombine/InstCombine.h
index ab4dc1c..247d791 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombine.h
+++ b/llvm/lib/Transforms/InstCombine/InstCombine.h
@@ -172,6 +172,8 @@
ConstantInt *DivRHS);
Instruction *FoldICmpShrCst(ICmpInst &ICI, BinaryOperator *DivI,
ConstantInt *DivRHS);
+ Instruction *FoldICmpCstShrCst(ICmpInst &I, Value *Op, Value *A,
+ ConstantInt *CI1, ConstantInt *CI2);
Instruction *FoldICmpAddOpCst(Instruction &ICI, Value *X, ConstantInt *CI,
ICmpInst::Predicate Pred);
Instruction *FoldGEPICmp(GEPOperator *GEPLHS, Value *RHS,