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

[apilipenko]

Summary

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.

[sanjoy]

lgtm

test/Transforms/CorrelatedValuePropagation/range.ll

460 ↗

(On Diff #67174)

Phabricator says there's a missing newline at the end of this file.

llvm/trunk/lib/Analysis/LazyValueInfo.cpp

if (LHS != Val)
     match(LHS, m_Add(m_Specific(Val), m_ConstantInt(Offset)));
 
   if (LHS == Val || Offset) {
     // Calculate the range of values that are allowed by the comparison
     ConstantRange RHSRange(RHS->getType()->getIntegerBitWidth(),
                            /*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 =
             isTrueDest ? Predicate : CmpInst::getInversePredicate(Predicate);
     ConstantRange TrueValues =
             ConstantRange::makeAllowedICmpRegion(Pred, RHSRange);
 
     if (Offset) // Apply the offset from above.

llvm/trunk/test/Transforms/CorrelatedValuePropagation/add.ll

 bb:
 ; CHECK: %add = add nsw i32 %a, 1
   %add = add i32 %a, 1
   br label %exit
 
 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/trunk/test/Transforms/CorrelatedValuePropagation/range.ll

then:
   %dead = icmp eq i32 %a, 8
   %alive = icmp eq i32 %a, 16
   %result = or i1 %dead, %alive
   ret i1 %result
 
 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
+}