llvm.noalias - ObjectSizeOffsetVisitor should look through them

[hfinkel]

Summary

This is part of the series started by D9375, and teaches ObjectSizeOffsetVisitor to look through llvm.noalias when it looks through bitcasts (which is only does via an initial stripping for some reason).

[reames]

Resigning as a reviewer to get a very stale review off my list of blocking tasks in phabricator. Please readd when desired.

[hfinkel]

This change should not be needed if the intrinsics are stripped by default.

lib/Analysis/MemoryBuiltins.cpp

ObjectSizeOffsetVisitor::ObjectSizeOffsetVisitor(const DataLayout &DL,
   // Pointer size must be rechecked for each object visited since it could have
   // a different address space.
 }
 
 SizeOffsetType ObjectSizeOffsetVisitor::compute(Value *V) {
   IntTyBits = DL.getPointerTypeSizeInBits(V->getType());
   Zero = APInt::getNullValue(IntTyBits);
 
-  V = V->stripPointerCasts();
+  V = V->stripPointerCasts(/*LookThroughNoAlias*/true);
   if (Instruction *I = dyn_cast<Instruction>(V)) {
     // If we have already seen this instruction, bail out. Cycles can happen in
     // unreachable code after constant propagation.
     if (!SeenInsts.insert(I).second)
       return unknown();
 
     if (GEPOperator *GEP = dyn_cast<GEPOperator>(V))
       return visitGEPOperator(*GEP);

 
 SizeOffsetEvalType ObjectSizeOffsetEvaluator::compute_(Value *V) {
   ObjectSizeOffsetVisitor Visitor(DL, TLI, Context, RoundToAlign);
   SizeOffsetType Const = Visitor.compute(V);
   if (Visitor.bothKnown(Const))
     return std::make_pair(ConstantInt::get(Context, Const.first),
                           ConstantInt::get(Context, Const.second));
 
-  V = V->stripPointerCasts();
+  V = V->stripPointerCasts(/*LookThroughNoAlias*/true);
 
   // check cache
   CacheMapTy::iterator CacheIt = CacheMap.find(V);
   if (CacheIt != CacheMap.end())
     return CacheIt->second;
 
   // always generate code immediately before the instruction being
   // processed, so that the generated code dominates the same BBs

test/Analysis/BasicAA/global-size.ll

define i16 @test1(i32* %P) {
         %X = load i16, i16* @B
         store i32 7, i32* %P
         %Y = load i16, i16* @B
         %Z = sub i16 %Y, %X
         ret i16 %Z
 ; CHECK: ret i16 0
 }
 
+; CHECK-LABEL: @test1a(
+define i16 @test1a(i32* %P) {
+        %b = call i16* @llvm.noalias.p0i16(i16* @B, metadata !1)
+        %X = load i16, i16* %b
+        store i32 7, i32* %P
+        %Y = load i16, i16* %b
+        %Z = sub i16 %Y, %X
+        ret i16 %Z
+; CHECK: ret i16 0
+}
+
 @B_as1 = addrspace(1) global i16 8
 
 define i16 @test1_as1(i32 addrspace(1)* %P) {
 ; CHECK-LABEL: @test1_as1(
 ; CHECK: ret i16 0
   %X = load i16, i16 addrspace(1)* @B_as1
   store i32 7, i32 addrspace(1)* %P
   %Y = load i16, i16 addrspace(1)* @B_as1
define i8 @test2(i32 %tmp79, i32 %w.2, i32 %indvar89) nounwind {
   %B = load i8, i8* %arrayidx412, align 1
   %C = sub i8 %A, %B
   ret i8 %C
 
 ; CHECK: %B = load i8
 ; CHECK: ret i8 %C
 }
 
+declare i16* @llvm.noalias.p0i16(i16*, metadata) nounwind
+
+!0 = !{!0, !"some domain"}
+!1 = !{!1, !0, !"some scope"}
+