[KeyInstr][Clang] Assign matrix element atom

This patch is part of a stack that teaches Clang to generate Key Instructions
metadata for C and C++.

The Key Instructions project is introduced, including a "quick summary" section
at the top which adds context for this PR, here:
https://discourse.llvm.org/t/rfc-improving-is-stmt-placement-for-better-interactive-debugging/82668

The feature is only functional in LLVM if LLVM is built with CMake flag
LLVM_EXPERIMENTAL_KEY_INSTRUCTIONs. Eventually that flag will be removed.

The Clang-side work is demoed here:
#130943

Author: OCHyams

clang/lib/CodeGen/CGExpr.cpp

@@ -2531,8 +2531,9 @@ void CodeGenFunction::EmitStoreThroughLValue(RValue Src, LValue Dst,
       llvm::Instruction *Load = Builder.CreateLoad(Dst.getMatrixAddress());
       llvm::Value *Vec =
           Builder.CreateInsertElement(Load, Src.getScalarVal(), Idx, "matins");
-      Builder.CreateStore(Vec, Dst.getMatrixAddress(),
-                          Dst.isVolatileQualified());
+      auto *I = Builder.CreateStore(Vec, Dst.getMatrixAddress(),
+                                    Dst.isVolatileQualified());
+      addInstToCurrentSourceAtom(I, Vec);
       return;
     }
 

clang/test/DebugInfo/KeyInstructions/agg.c

@@ -5,6 +5,8 @@
 // RUN: | FileCheck %s --implicit-check-not atomGroup --implicit-check-not atomRank
 
 __attribute__((ext_vector_type(1))) char c;
+typedef float m5x5 __attribute__((matrix_type(5, 5)));
+m5x5 m;
 typedef struct { int a, b, c; } Struct;
 void fun(Struct a) {
 // CHECK: call void @llvm.memcpy{{.*}}, !dbg [[G1R1:!.*]]
@@ -17,9 +19,16 @@ void fun(Struct a) {
 // CHECK: %vecins = insertelement <1 x i8> %2, i8 0, i32 0, !dbg [[G3R2:!.*]]
 // CHECK: store <1 x i8> %vecins, ptr @c{{.*}}, !dbg [[G3R1:!.*]]
   c[0] = 0;
+
+// CHECK: %3 = load <25 x float>, ptr @m, align 4
+// CHECK: %matins = insertelement <25 x float> %3, float 0.000000e+00, i64 0, !dbg [[G4R2:!.*]]
+// CHECK: store <25 x float> %matins, ptr @m{{.*}}, !dbg [[G4R1:!.*]]
+  m[0][0] = 0;
 }
 
 // CHECK: [[G1R1]] = !DILocation({{.*}}, atomGroup: 1, atomRank: 1)
 // CHECK: [[G2R1]] = !DILocation({{.*}}, atomGroup: 2, atomRank: 1)
 // CHECK: [[G3R2]] = !DILocation({{.*}}, atomGroup: 3, atomRank: 2)
 // CHECK: [[G3R1]] = !DILocation({{.*}}, atomGroup: 3, atomRank: 1)
+// CHECK: [[G4R2]] = !DILocation({{.*}}, atomGroup: 4, atomRank: 2)
+// CHECK: [[G4R1]] = !DILocation({{.*}}, atomGroup: 4, atomRank: 1)