[llvm] AMDGPU: Respect target assembler directives over command line (PR #207812)

[Matt Arsenault via llvm-commits]

================
@@ -5989,14 +6001,48 @@ bool AMDGPUAsmParser::ParseDirectiveAMDGCNTarget() {
   const std::optional<AMDGPU::TargetID> &CurrentTargetID =
       getTargetStreamer().getTargetID();
 
-  if (*CurrentTargetID != ParsedTargetID) {
+  Triple DirectiveTriple(ParsedTargetID.getTargetTripleString());
+  const Triple &STITriple = getSTI().getTargetTriple();
+  if (!DirectiveTriple.isCompatibleWith(STITriple)) {
     return getParser().Error(
-        TargetStart, Twine(".amdgcn_target directive's target id ") +
-                         Twine(ParsedTargetID.toString()) +
-                         Twine(" does not match the specified target id ") +
+        TargetStart, ".amdgcn_target " + Twine(ParsedTargetID.toString()) +
+                         " is incompatible with " +
                          Twine(CurrentTargetID->toString()));
   }
 
+  // Error if the ISA version doesn't match
+  AMDGPU::IsaVersion DirectiveISA = AMDGPU::getIsaVersion(
+      AMDGPU::getArchNameAMDGCN(ParsedTargetID.getGPUKind()));
+  AMDGPU::IsaVersion CurrentISA = AMDGPU::getIsaVersion(getSTI().getCPU());
+  if (DirectiveISA != CurrentISA) {
+    return getParser().Error(
+        TargetStart, ".amdgcn_target " + Twine(ParsedTargetID.toString()) +
+                         " does not match the specified target id " +
+                         Twine(CurrentTargetID->toString()));
+  }
+
+  // Warn if sramecc or xnack mismatch. These do not change the encoding.
+  if (AMDGPU::IsaInfo::targetIDSettingsConflict(
+          ParsedTargetID.getXnackSetting(),
+          CurrentTargetID->getXnackSetting())) {
+    Warning(TargetStart,
+            ".amdgcn_target directive has conflicting xnack settings");
+  }
+  if (AMDGPU::IsaInfo::targetIDSettingsConflict(
+          ParsedTargetID.getSramEccSetting(),
+          CurrentTargetID->getSramEccSetting())) {
+    Warning(TargetStart,
+            ".amdgcn_target directive has conflicting sramecc settings");
+  }
+
+  // Update the target streamer's TargetID with settings from the directive.
+  // We don't update the MCSubtargetInfo because we've already validated
+  // that the directive matches the command-line CPU.
----------------
arsenm wrote:

I changed my mind on this several times. My original goal was to eliminate dependency on the xnack/sramecc features, so this PR ended up on only weakening mismatch on xnack/sramecc. This is worth revisiting after the sub arch patches have landed for a while 

https://github.com/llvm/llvm-project/pull/207812