From fcb9926813ef9bd18bf2b3aab4ab58c6522c2c5e Mon Sep 17 00:00:00 2001 From: Rafael Espindola Date: Fri, 30 May 2014 15:54:32 +0000 Subject: [PATCH] PR19753: Optimize comparisons with "ashr exact" of a constanst. Patch by suyog sarda. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209903 91177308-0d34-0410-b5e6-96231b3b80d8 --- .../InstCombine/InstCombineCompares.cpp | 17 +++++++++++++++++ test/Transforms/InstCombine/icmp.ll | 8 ++++++++ 2 files changed, 25 insertions(+) diff --git a/lib/Transforms/InstCombine/InstCombineCompares.cpp b/lib/Transforms/InstCombine/InstCombineCompares.cpp index 02e8bf10135..79cd1fba85f 100644 --- a/lib/Transforms/InstCombine/InstCombineCompares.cpp +++ b/lib/Transforms/InstCombine/InstCombineCompares.cpp @@ -2439,6 +2439,23 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) { return new ICmpInst(I.getPredicate(), A, B); } + // PR19753: + // (icmp (ashr exact const2, A), const1) -> icmp A, Log2(const2/const1) + // Cases where const1 doesn't divide const2 exactly or Quotient is not + // exact of log2 are handled by SimplifyICmpInst call above where we + // return false. + // TODO: Handle this for lshr exact with udiv. + { + ConstantInt *CI2; + if (match(Op0, m_AShr(m_ConstantInt(CI2), m_Value(A))) && + (cast(Op0)->isExact())) { + APInt Quotient = CI2->getValue().sdiv(CI->getValue()); + unsigned shift = Quotient.logBase2(); + return new ICmpInst(I.getPredicate(), A, + ConstantInt::get(A->getType(), shift)); + } + } + // If we have an icmp le or icmp ge instruction, turn it into the // appropriate icmp lt or icmp gt instruction. This allows us to rely on // them being folded in the code below. The SimplifyICmpInst code has diff --git a/test/Transforms/InstCombine/icmp.ll b/test/Transforms/InstCombine/icmp.ll index f45897cd3ee..fd7514d9e17 100644 --- a/test/Transforms/InstCombine/icmp.ll +++ b/test/Transforms/InstCombine/icmp.ll @@ -1365,3 +1365,11 @@ define i1 @icmp_neg_cst_slt(i32 %a) { %2 = icmp slt i32 %1, -10 ret i1 %2 } + +; CHECK-LABEL: @exact_ashr_eq_false +; CHECK-NEXT: icmp eq i32 %a, 1 +define i1 @exact_ashr_eq_false(i32 %a) { + %shr = ashr exact i32 -30, %a + %cmp = icmp eq i32 %shr, -15 + ret i1 %cmp +} -- 2.34.1