[LVI] Support for ashr in LVI

[jskumari]

Summary

Enhance LVI to analyze the ‘ashr’ binary operation. This leverages the infrastructure in ConstantRange for the ashr operation.

[anna]

lgtm.

[jskumari]

Updating the patch to reflect correct path names.

llvm/trunk/lib/Analysis/LazyValueInfo.cpp

bool LazyValueInfoImpl::solveBlockValueBinaryOp(ValueLatticeElement &BBLV,
   // we're not going to be able to get any useful information anyways.
   switch (BO->getOpcode()) {
   case Instruction::Add:
   case Instruction::Sub:
   case Instruction::Mul:
   case Instruction::UDiv:
   case Instruction::Shl:
   case Instruction::LShr:
+  case Instruction::AShr:
   case Instruction::And:
   case Instruction::Or:
     // continue into the code below
     break;
   default:
     // Unhandled instructions are overdefined.
     DEBUG(dbgs() << " compute BB '" << BB->getName()
                  << "' - overdefined (unknown binary operator).\n");

llvm/trunk/test/Analysis/LazyValueAnalysis/lvi-for-ashr.ll

+; RUN: opt -correlated-propagation -S %s | FileCheck %s
+; CHECK-LABEL: @test-ashr
+; CHECK: bb_then
+; CHECK:  %. = select i1 true, i32 3, i32 2
+define i32 @test-ashr(i32 %c) {
+chk65:
+  %cmp = icmp sgt i32 %c, 65
+  br i1 %cmp, label %return, label %chk0
+
+chk0:
+  %cmp1 = icmp slt i32 %c, 0
+  br i1 %cmp, label %return, label %bb_if
+
+bb_if:
+  %ashr.val = ashr exact i32 %c, 2
+  %cmp2 = icmp sgt i32 %ashr.val, 15
+  br i1 %cmp2, label %bb_then, label %return
+
+bb_then:
+  %cmp3 = icmp eq i32 %ashr.val, 16
+  %. = select i1 %cmp3, i32 3, i32 2
+  br label %return
+
+return:
+  %retval = phi i32 [0, %chk65], [1, %chk0], [%., %bb_then], [4, %bb_if]
+  ret i32 %retval
+}