add implicit trunc warnings

Author: farzonl

clang/include/clang/Basic/DiagnosticSemaKinds.td

@@ -4338,6 +4338,9 @@ def warn_param_typestate_mismatch : Warning<
 def warn_unknown_sanitizer_ignored : Warning<
   "unknown sanitizer '%0' ignored">, InGroup<UnknownSanitizers>;
 
+def warn_impcast_matrix_scalar : Warning<
+  "implicit conversion turns matrix to scalar: %0 to %1">,
+  InGroup<Conversion>, DefaultIgnore;
 def warn_impcast_vector_scalar : Warning<
   "implicit conversion turns vector to scalar: %0 to %1">,
   InGroup<Conversion>, DefaultIgnore;
@@ -13245,6 +13248,9 @@ def err_hlsl_builtin_scalar_vector_mismatch
 def warn_hlsl_impcast_vector_truncation : Warning<
   "implicit conversion truncates vector: %0 to %1">, InGroup<Conversion>;
 
+def warn_hlsl_impcast_matrix_truncation : Warning<
+  "implicit conversion truncates matrix: %0 to %1">, InGroup<Conversion>;
+
 def warn_hlsl_availability : Warning<
   "%0 is only available %select{|in %4 environment }3on %1 %2 or newer">,
   InGroup<HLSLAvailability>, DefaultError;

clang/lib/Sema/SemaChecking.cpp

@@ -37,6 +37,7 @@
 #include "clang/AST/TemplateBase.h"
 #include "clang/AST/TemplateName.h"
 #include "clang/AST/Type.h"
+#include "clang/AST/TypeBase.h"
 #include "clang/AST/TypeLoc.h"
 #include "clang/AST/UnresolvedSet.h"
 #include "clang/Basic/AddressSpaces.h"
@@ -12586,6 +12587,19 @@ void Sema::CheckImplicitConversion(Expr *E, QualType T, SourceLocation CC,
   if (auto VecTy = dyn_cast<VectorType>(Target))
     Target = VecTy->getElementType().getTypePtr();
 
+  if (isa<ConstantMatrixType>(Source)) {
+    if (!isa<ConstantMatrixType>(Target)) {
+      return DiagnoseImpCast(*this, E, T, CC, diag::warn_impcast_matrix_scalar);
+    } else if (getLangOpts().HLSL &&
+               Target->castAs<ConstantMatrixType>()->getNumElementsFlattened() <
+                   Source->castAs<ConstantMatrixType>()
+                       ->getNumElementsFlattened()) {
+      // Diagnose Matrix truncation but don't return. We may also want to
+      // diagnose an element conversion.
+      DiagnoseImpCast(*this, E, T, CC,
+                      diag::warn_hlsl_impcast_matrix_truncation);
+    }
+  }
   // Strip complex types.
   if (isa<ComplexType>(Source)) {
     if (!isa<ComplexType>(Target)) {

clang/test/SemaHLSL/Types/BuiltinMatrix/MatrixImplicitTruncCastWarnings.hlsl

@@ -0,0 +1,50 @@
+// RUN: %clang_cc1 -triple dxil-pc-shadermodel6.6-library -finclude-default-header -Wconversion -verify %s
+
+export int3x4 trunc_cast(int4x4 i44) {
+    int3x4 i34 = i44;
+    // expected-warning@-1{{implicit conversion truncates matrix: 'int4x4' (aka 'matrix<int, 4, 4>') to 'matrix<int, 3, 4>'}}
+    return i34;
+}
+
+export int4x3 trunc_cast0(int4x4 i44) {
+    int4x3 i43 = i44;
+    // expected-warning@-1{{implicit conversion truncates matrix: 'int4x4' (aka 'matrix<int, 4, 4>') to 'matrix<int, 4, 3>'}}
+    return i43;
+}
+
+export int3x3 trunc_cast1(int4x4 i44) {
+    int3x3 i33 = i44;
+    // expected-warning@-1{{implicit conversion truncates matrix: 'int4x4' (aka 'matrix<int, 4, 4>') to 'matrix<int, 3, 3>'}}
+    return i33;
+}
+
+export int3x2 trunc_cast2(int4x4 i44) {
+    int3x2 i32 = i44;
+    // expected-warning@-1{{implicit conversion truncates matrix: 'int4x4' (aka 'matrix<int, 4, 4>') to 'matrix<int, 3, 2>'}}
+    return i32;
+}
+
+export int2x3 trunc_cast3(int4x4 i44) {
+    int2x3 i23 = i44;
+    // expected-warning@-1{{implicit conversion truncates matrix: 'int4x4' (aka 'matrix<int, 4, 4>') to 'matrix<int, 2, 3>'}}
+    return i23;
+}
+
+export int2x2 trunc_cast4(int4x4 i44) {
+    int2x2 i22 = i44;
+    // expected-warning@-1{{implicit conversion truncates matrix: 'int4x4' (aka 'matrix<int, 4, 4>') to 'matrix<int, 2, 2>'}}
+    return i22;
+}
+
+export int2x1 trunc_cast5(int4x4 i44) {
+    int2x1 i21 = i44;
+    // expected-warning@-1{{implicit conversion truncates matrix: 'int4x4' (aka 'matrix<int, 4, 4>') to 'matrix<int, 2, 1>'}}
+    return i21;
+}
+
+export int trunc_scalar_cast6(int4x4 i44) {
+    int i1 = i44;
+    // expected-warning@-1{{implicit conversion turns matrix to scalar: 'int4x4' (aka 'matrix<int, 4, 4>') to 'int'}}
+    return i1;
+}
+