Update validator diagnostics with "structurally dominated" (#4844)

The updated rules in SPIR-V 1.6 Rev2 use structural dominance,
so update the messages to match
diff --git a/source/val/validate_cfg.cpp b/source/val/validate_cfg.cpp
index 9806462..506b5e5 100644
--- a/source/val/validate_cfg.cpp
+++ b/source/val/validate_cfg.cpp
@@ -553,7 +553,7 @@
           !header->structurally_dominates(*target_block)) {
         return _.diag(SPV_ERROR_INVALID_CFG, header->label())
                << "Selection header " << _.getIdName(header->id())
-               << " does not dominate its case construct "
+               << " does not structurally dominate its case construct "
                << _.getIdName(target);
       }
 
@@ -742,15 +742,15 @@
       return _.diag(SPV_ERROR_INVALID_CFG, _.FindDef(merge->id()))
              << ConstructErrorString(construct, _.getIdName(header->id()),
                                      _.getIdName(merge->id()),
-                                     "does not dominate");
+                                     "does not structurally dominate");
     }
     // If it's really a merge block for a selection or loop, then it must be
-    // *strictly* dominated by the header.
+    // *strictly* structrually dominated by the header.
     if (construct.ExitBlockIsMergeBlock() && (header == merge)) {
       return _.diag(SPV_ERROR_INVALID_CFG, _.FindDef(merge->id()))
              << ConstructErrorString(construct, _.getIdName(header->id()),
                                      _.getIdName(merge->id()),
-                                     "does not strictly dominate");
+                                     "does not strictly structurally dominate");
     }
 
     // Check post-dominance for continue constructs.  But dominance and
@@ -760,7 +760,7 @@
         return _.diag(SPV_ERROR_INVALID_CFG, _.FindDef(merge->id()))
                << ConstructErrorString(construct, _.getIdName(header->id()),
                                        _.getIdName(merge->id()),
-                                       "is not post dominated by");
+                                       "is not structurally post dominated by");
       }
     }
 
diff --git a/test/val/val_cfg_test.cpp b/test/val/val_cfg_test.cpp
index afab3be..2423b1e 100644
--- a/test/val/val_cfg_test.cpp
+++ b/test/val/val_cfg_test.cpp
@@ -663,7 +663,8 @@
     EXPECT_THAT(
         getDiagnosticString(),
         MatchesRegex("The selection construct with the selection header "
-                     ".\\[%head\\] does not strictly dominate the merge block "
+                     ".\\[%head\\] does not strictly structurally dominate the "
+                     "merge block "
                      ".\\[%head\\]\n  %head = OpLabel\n"));
   } else {
     ASSERT_EQ(SPV_SUCCESS, ValidateInstructions()) << str;
@@ -1345,11 +1346,13 @@
   CompileSuccessfully(str);
   if (GetParam() == SpvCapabilityShader) {
     ASSERT_EQ(SPV_ERROR_INVALID_CFG, ValidateInstructions());
-    EXPECT_THAT(getDiagnosticString(),
-                MatchesRegex("The continue construct with the continue target "
-                             ".\\[%loop1_cont\\] is not post dominated by the "
-                             "back-edge block .\\[%be_block\\]\n"
-                             "  %be_block = OpLabel\n"));
+    EXPECT_THAT(
+        getDiagnosticString(),
+        MatchesRegex(
+            "The continue construct with the continue target "
+            ".\\[%loop1_cont\\] is not structurally post dominated by the "
+            "back-edge block .\\[%be_block\\]\n"
+            "  %be_block = OpLabel\n"));
   } else {
     ASSERT_EQ(SPV_SUCCESS, ValidateInstructions());
   }
@@ -1485,10 +1488,11 @@
   if (is_shader) {
     ASSERT_EQ(SPV_ERROR_INVALID_CFG, ValidateInstructions());
     EXPECT_THAT(getDiagnosticString(),
-                MatchesRegex("The continue construct with the continue target "
-                             ".\\[%cheader\\] is not post dominated by the "
-                             "back-edge block .\\[%be_block\\]\n"
-                             "  %be_block = OpLabel\n"));
+                MatchesRegex(
+                    "The continue construct with the continue target "
+                    ".\\[%cheader\\] is not structurally post dominated by the "
+                    "back-edge block .\\[%be_block\\]\n"
+                    "  %be_block = OpLabel\n"));
   } else {
     ASSERT_EQ(SPV_SUCCESS, ValidateInstructions());
   }
@@ -1517,11 +1521,12 @@
   CompileSuccessfully(str);
   if (is_shader) {
     ASSERT_EQ(SPV_ERROR_INVALID_CFG, ValidateInstructions());
-    EXPECT_THAT(getDiagnosticString(),
-                MatchesRegex("The continue construct with the continue target "
-                             ".\\[%loop\\] is not post dominated by the "
-                             "back-edge block .\\[%cont\\]\n"
-                             "  %cont = OpLabel\n"))
+    EXPECT_THAT(
+        getDiagnosticString(),
+        MatchesRegex("The continue construct with the continue target "
+                     ".\\[%loop\\] is not structurally post dominated by the "
+                     "back-edge block .\\[%cont\\]\n"
+                     "  %cont = OpLabel\n"))
         << str;
   } else {
     ASSERT_EQ(SPV_SUCCESS, ValidateInstructions());
@@ -1553,11 +1558,12 @@
   CompileSuccessfully(str);
   if (is_shader) {
     ASSERT_EQ(SPV_ERROR_INVALID_CFG, ValidateInstructions());
-    EXPECT_THAT(getDiagnosticString(),
-                MatchesRegex("The continue construct with the continue target "
-                             ".\\[%loop\\] is not post dominated by the "
-                             "back-edge block .\\[%cont\\]\n"
-                             "  %cont = OpLabel\n"));
+    EXPECT_THAT(
+        getDiagnosticString(),
+        MatchesRegex("The continue construct with the continue target "
+                     ".\\[%loop\\] is not structurally post dominated by the "
+                     "back-edge block .\\[%cont\\]\n"
+                     "  %cont = OpLabel\n"));
   } else {
     ASSERT_EQ(SPV_SUCCESS, ValidateInstructions());
   }
@@ -3200,7 +3206,7 @@
   EXPECT_THAT(
       getDiagnosticString(),
       HasSubstr("The continue construct with the continue target 9[%9] is not "
-                "post dominated by the back-edge block 13[%13]"));
+                "structurally post dominated by the back-edge block 13[%13]"));
 }
 
 TEST_F(ValidateCFG, BreakFromSwitch) {
@@ -4208,9 +4214,11 @@
 
   CompileSuccessfully(text);
   EXPECT_NE(SPV_SUCCESS, ValidateInstructions());
-  EXPECT_THAT(getDiagnosticString(),
-              HasSubstr("The selection construct with the selection header "
-                        "8[%8] does not dominate the merge block 10[%10]\n"));
+  EXPECT_THAT(
+      getDiagnosticString(),
+      HasSubstr(
+          "The selection construct with the selection header "
+          "8[%8] does not structurally dominate the merge block 10[%10]\n"));
 }
 
 TEST_F(ValidateCFG, UnreachableIsStaticallyReachable) {