[clang] [Matrix] Preserve signedness when extending matrix index expression. (PR #103044)

[Florian Hahn via cfe-commits]

https://github.com/fhahn created https://github.com/llvm/llvm-project/pull/103044

As per [1] the indices for a matrix element access operator shall have integral or unscoped enumeration types and be non-negative. At the moment, the index expression is converted to SizeType irrespective of the signedness of the index expression. This causes implicit sign conversion warnings if any of the indices is signed.

As per the spec, using signed types as indices is allowed and should not cause any warnings. If the index expression is signed, extend to SignedSizeType to avoid the warning.

[1] https://clang.llvm.org/docs/MatrixTypes.html#matrix-type-element-access-operator

>From 4902d2088ced06629108dd9ae59aaa0d6bdeaf79 Mon Sep 17 00:00:00 2001
From: Florian Hahn <flo at fhahn.com>
Date: Tue, 13 Aug 2024 12:28:34 +0100
Subject: [PATCH] [Matrix] Preserve signedness when extending matrix index
 expression.

As per [1] the indices for a matrix element access operator shall have integral
or unscoped enumeration types and be non-negative. At the moment, the
index expression is converted to SizeType irrespective of the signedness
of the index expression. This causes implicit sign conversion warnings
if any of the indices is signed.

As per the spec, using signed types as indices is allowed and should not
cause any warnings. If the index expression is signed, extend to
SignedSizeType to avoid the warning.

[1] https://clang.llvm.org/docs/MatrixTypes.html#matrix-type-element-access-operator
---
 clang/lib/Sema/SemaExpr.cpp                                | 6 ++++--
 .../test/SemaCXX/matrix-index-operator-sign-conversion.cpp | 7 ++-----
 2 files changed, 6 insertions(+), 7 deletions(-)

diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 8defc8e1c185c0..e2c620f0260140 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -5021,8 +5021,10 @@ ExprResult Sema::CreateBuiltinMatrixSubscriptExpr(Expr *Base, Expr *RowIdx,
       }
     }
 
-    ExprResult ConvExpr =
-        tryConvertExprToType(IndexExpr, Context.getSizeType());
+    ExprResult ConvExpr = tryConvertExprToType(
+        IndexExpr, IndexExpr->getType()->isSignedIntegerType()
+                       ? Context.getSignedSizeType()
+                       : Context.getSizeType());
     assert(!ConvExpr.isInvalid() &&
            "should be able to convert any integer type to size type");
     return ConvExpr.get();
diff --git a/clang/test/SemaCXX/matrix-index-operator-sign-conversion.cpp b/clang/test/SemaCXX/matrix-index-operator-sign-conversion.cpp
index 4254780651c5f5..e6fe4a6c57ff22 100644
--- a/clang/test/SemaCXX/matrix-index-operator-sign-conversion.cpp
+++ b/clang/test/SemaCXX/matrix-index-operator-sign-conversion.cpp
@@ -2,19 +2,16 @@
 
 template <typename T, int R, int C> using m __attribute__((__matrix_type__(R,C))) = T;
 
-// FIXME: should not warn here.
 double index1(m<double,3,1> X, int      i) { return X[i][0]; }
-// expected-warning at -1 {{implicit conversion changes signedness: 'int' to 'unsigned long'}}
 
 double index2(m<double,3,1> X, unsigned i) { return X[i][0]; }
 
 double index3(m<double,3,1> X, char     i) { return X[i][0]; }
-// expected-warning at -1 {{implicit conversion changes signedness: 'char' to 'unsigned long'}}
 
 double index4(m<double,3,1> X, int      i) { return X[0][i]; }
-// expected-warning at -1 {{implicit conversion changes signedness: 'int' to 'unsigned long'}}
 
 double index5(m<double,3,1> X, unsigned i) { return X[0][i]; }
 
 double index6(m<double,3,1> X, char     i) { return X[0][i]; }
-// expected-warning at -1 {{implicit conversion changes signedness: 'char' to 'unsigned long'}}
+
+// expected-no-diagnostics