[LVI] Take range metadata into account while calculating icmp condition constraints

Take range metadata into account for conditions like this:

%length = load i32, i32* %length_ptr, !range !{i32 0, i32 2147483647}
%cmp = icmp ult i32 %a, %length

This is a common pattern for range checks where the length of the array is dynamically loaded.

Reviewed By: sanjoy

Differential Revision: https://reviews.llvm.org/D23267

llvm-svn: 278496

llvm/lib/Analysis/LazyValueInfo.cpp

@@ -1211,6 +1211,9 @@ static LVILatticeVal getValueFromICmpCondition(Value *Val, ICmpInst *ICI,
                            /*isFullSet=*/true);
     if (ConstantInt *CI = dyn_cast<ConstantInt>(RHS))
       RHSRange = ConstantRange(CI->getValue());
+    else if (Instruction *I = dyn_cast<Instruction>(RHS))
+      if (auto *Ranges = I->getMetadata(LLVMContext::MD_range))
+        RHSRange = getConstantRangeFromMetadata(*Ranges);
 
     // If we're interested in the false dest, invert the condition
     CmpInst::Predicate Pred =

llvm/test/Transforms/CorrelatedValuePropagation/add.ll

@@ -193,3 +193,22 @@ bb:
 exit:
   ret void
 }
+
+@limit = external global i32
+; CHECK-LABEL: @test11(
+define i32 @test11(i32* %p, i32 %i) {
+  %limit = load i32, i32* %p, !range !{i32 0, i32 2147483647}
+  %within.1 = icmp ugt i32 %limit, %i
+  %i.plus.7 = add i32 %i, 7
+  %within.2 = icmp ugt i32 %limit, %i.plus.7
+  %within = and i1 %within.1, %within.2
+  br i1 %within, label %then, label %else
+
+then:
+; CHECK: %i.plus.6 = add nuw nsw i32 %i, 6
+  %i.plus.6 = add i32 %i, 6
+  ret i32 %i.plus.6
+
+else:
+  ret i32 0
+}

llvm/test/Transforms/CorrelatedValuePropagation/range.ll

@@ -445,3 +445,20 @@ then:
 else:
   ret i1 false
 }
+
+@limit = external global i32
+define i1 @test15(i32 %a) {
+; CHECK-LABEL: @test15(
+; CHECK: then:
+; CHECK-NEXT: ret i1 false
+  %limit = load i32, i32* @limit, !range !{i32 0, i32 256}
+  %cmp = icmp ult i32 %a, %limit
+  br i1 %cmp, label %then, label %else
+
+then:
+  %result = icmp eq i32 %a, 255
+  ret i1 %result
+
+else:
+  ret i1 false
+}