[PATCH] D32260: [TBAA] Vector types should (only) alias with their element types

[Hal Finkel via Phabricator via cfe-commits]

hfinkel abandoned this revision.
hfinkel added a comment.

@rjmccall said, on this topic, in https://reviews.llvm.org/D31885:

> The root problem there is that the design of vector types and vector 
> interfaces is generally quite bad; you cannot rely on things like vectors 
> being stored with an appropriate element type for whatever value the user is 
> actually trying to work with.



> For example, Clang's xmmintrin.h specifies that __m128 is a vector of 4 ints. 
>  How confident are you that that type is never used to store a vector of 4 
> floats?  Keep in mind that the compiler allows __m128 to freely implicitly 
> convert to __v4sf.

And I think he's right; we probably can't do this in general. vector types 
really are just bags of bits on many platforms ;)


https://reviews.llvm.org/D32260



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[PATCH] D32260: [TBAA] Vector types should (only) alias with their element types

[Hal Finkel via Phabricator via cfe-commits]

hfinkel created this revision.
Herald added a subscriber: mcrosier.

Currently, all of our builtin vector types are equivalent to char for TBAA 
purposes. It would be useful to make this less conservative. This patch makes 
vector types equivalent to their element types for type-aliasing purposes. I 
think it's common for programmers to assume that they can cast freely between 
the vector types and the scalar types (so long as they're being sufficiently 
careful about alignments), and we should certainly preserve that model. Given 
that we assume that int* and float* don't alias, I don't think we need to 
assume that int* and vec_of_float* alias or vec_of_int* and vec_of_float* alias.

The cases I've seen where I know this would be helpful involve integral scalar 
pointers and floating-point vector pointers, so I'm generalizing a bit here. If 
this would break too much code, one option is fall back to doing this only for 
floating-point types. That having been said, I know that it is common on some 
platforms to case between floating-point vectors and integer vectors in order 
to implement operations like fabs, and maybe that makes this untenable on those 
platforms?

Thoughts?


https://reviews.llvm.org/D32260

Files:
  lib/CodeGen/CodeGenTBAA.cpp
  test/CodeGen/tbaa-vector.cpp


Index: test/CodeGen/tbaa-vector.cpp
===
--- /dev/null
+++ test/CodeGen/tbaa-vector.cpp
@@ -0,0 +1,17 @@
+// RUN: %clang_cc1 -triple x86_64-apple-darwin -O1 -no-struct-path-tbaa 
-disable-llvm-passes %s -emit-llvm -o - | FileCheck %s
+
+typedef double __m256d __attribute__((__vector_size__(32)));
+__m256d foo(double *x, __m256d *y) {
+  *x = 0.0;
+  return *y;
+
+// CHECK-LABEL: define <4 x double> @_Z3fooPdPDv4_d
+// CHECK: store double 0.00e+00, double* %{{.*}}, align 8, !tbaa 
[[TAG_double:!.*]]
+// CHECK: load <4 x double>, <4 x double>* %{{.*}}, align {{.*}}, !tbaa 
[[TAG_double]]
+}
+
+// CHECK: [[TYPE_char:!.*]] = !{!"omnipotent char", [[TAG_cxx_tbaa:!.*]],
+// CHECK: [[TAG_cxx_tbaa]] = !{!"Simple C++ TBAA"}
+// CHECK: [[TAG_double]] = !{[[TYPE_double:!.*]], [[TYPE_double]], i64 0}
+// CHECK: [[TYPE_double]] = !{!"double", [[TYPE_char]],
+
Index: lib/CodeGen/CodeGenTBAA.cpp
===
--- lib/CodeGen/CodeGenTBAA.cpp
+++ lib/CodeGen/CodeGenTBAA.cpp
@@ -101,6 +101,10 @@
   if (TypeHasMayAlias(QTy))
 return getChar();
 
+  // Vector types should alias with their element types.
+  if (auto *VT = QTy->getAs())
+QTy = VT->getElementType();
+
   const Type *Ty = Context.getCanonicalType(QTy).getTypePtr();
 
   if (llvm::MDNode *N = MetadataCache[Ty])


Index: test/CodeGen/tbaa-vector.cpp
===
--- /dev/null
+++ test/CodeGen/tbaa-vector.cpp
@@ -0,0 +1,17 @@
+// RUN: %clang_cc1 -triple x86_64-apple-darwin -O1 -no-struct-path-tbaa -disable-llvm-passes %s -emit-llvm -o - | FileCheck %s
+
+typedef double __m256d __attribute__((__vector_size__(32)));
+__m256d foo(double *x, __m256d *y) {
+  *x = 0.0;
+  return *y;
+
+// CHECK-LABEL: define <4 x double> @_Z3fooPdPDv4_d
+// CHECK: store double 0.00e+00, double* %{{.*}}, align 8, !tbaa [[TAG_double:!.*]]
+// CHECK: load <4 x double>, <4 x double>* %{{.*}}, align {{.*}}, !tbaa [[TAG_double]]
+}
+
+// CHECK: [[TYPE_char:!.*]] = !{!"omnipotent char", [[TAG_cxx_tbaa:!.*]],
+// CHECK: [[TAG_cxx_tbaa]] = !{!"Simple C++ TBAA"}
+// CHECK: [[TAG_double]] = !{[[TYPE_double:!.*]], [[TYPE_double]], i64 0}
+// CHECK: [[TYPE_double]] = !{!"double", [[TYPE_char]],
+
Index: lib/CodeGen/CodeGenTBAA.cpp
===
--- lib/CodeGen/CodeGenTBAA.cpp
+++ lib/CodeGen/CodeGenTBAA.cpp
@@ -101,6 +101,10 @@
   if (TypeHasMayAlias(QTy))
 return getChar();
 
+  // Vector types should alias with their element types.
+  if (auto *VT = QTy->getAs())
+QTy = VT->getElementType();
+
   const Type *Ty = Context.getCanonicalType(QTy).getTypePtr();
 
   if (llvm::MDNode *N = MetadataCache[Ty])
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