noalias for params, inbounds for GEPs

These don't get us to be able to hoist uniforms yet,
but I think they're required.  Tests still pass.

The nullptrs in the CreateGEP calls were implied by
the old special cases we were calling before.  They
mean, pick up the type from the pointer argument.

Change-Id: Idd2b5c4b782229ebf2640f87e0ed6ebb63809042
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/274583
Reviewed-by: Herb Derby <herb@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>

Author: Mike Klein

src/core/SkVM.cpp

@@ -1924,6 +1924,9 @@ namespace skvm {
                                                               arg_types, /*vararg?=*/false);
         llvm::Function* fn
             = llvm::Function::Create(fn_type, llvm::GlobalValue::ExternalLinkage, debug_name, *mod);
+        for (size_t i = 0; i < fStrides.size(); i++) {
+            fn->addParamAttr(i+1, llvm::Attribute::NoAlias);
+        }
 
         llvm::BasicBlock *enter = llvm::BasicBlock::Create(ctx, "enter", fn),
                          *testK = llvm::BasicBlock::Create(ctx, "testK", fn),
@@ -1995,7 +1998,9 @@ namespace skvm {
                 case Op::uniform16: t = i16; goto uniform;
                 case Op::uniform32: t = i32; goto uniform;
                 uniform: {
-                    llvm::Value* ptr = b->CreateBitCast(b->CreateConstGEP1_32(args[immy], immz),
+                    llvm::Value* ptr = b->CreateBitCast(b->CreateConstInBoundsGEP1_32(nullptr,
+                                                                                      args[immy],
+                                                                                      immz),
                                                         t->getPointerTo());
                     llvm::Value* val = b->CreateZExt(b->CreateAlignedLoad(ptr, 1), i32);
                     vals[i] = I32->isVectorTy() ? b->CreateVectorSplat(K, val)
@@ -2008,10 +2013,12 @@ namespace skvm {
                 gather: {
                     // Our gather base pointer is immz bytes off of uniform immy.
                     llvm::Value* base =
-                        b->CreateLoad(b->CreateBitCast(b->CreateConstGEP1_32(args[immy], immz),
+                        b->CreateLoad(b->CreateBitCast(b->CreateConstInBoundsGEP1_32(nullptr,
+                                                                                     args[immy],
+                                                                                     immz),
                                                        t->getPointerTo()->getPointerTo()));
 
-                    llvm::Value* ptr = b->CreateGEP(base, vals[x]);
+                    llvm::Value* ptr = b->CreateInBoundsGEP(nullptr, base, vals[x]);
                     llvm::Value* gathered;
                     if (ptr->getType()->isVectorTy()) {
                         gathered = b->CreateMaskedGather(ptr, 1);
@@ -2189,7 +2196,8 @@ namespace skvm {
 
             // Each arg ptr += K
             for (size_t i = 0; i < fStrides.size(); i++) {
-                llvm::Value* arg_next = b.CreateGEP(args[i], b.getInt32(K*fStrides[i]));
+                llvm::Value* arg_next
+                    = b.CreateConstInBoundsGEP1_32(nullptr, args[i], K*fStrides[i]);
                 args[i]->addIncoming(arg_next, loopK);
             }
             b.CreateBr(testK);
@@ -2229,7 +2237,8 @@ namespace skvm {
 
             // Each arg ptr += K
             for (size_t i = 0; i < fStrides.size(); i++) {
-                llvm::Value* arg_next = b.CreateGEP(args[i], b.getInt32(fStrides[i]));
+                llvm::Value* arg_next
+                    = b.CreateConstInBoundsGEP1_32(nullptr, args[i], fStrides[i]);
                 args[i]->addIncoming(arg_next, loop1);
             }
             b.CreateBr(test1);