ac/llvm: don't create the target machine if the LLVM processor is unsupported

If a processor is unsupported, LLVM chooses "tahiti", which hangs
everything except gfx6. Check for support manually.

Reviewed-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16112>

src/amd/llvm/ac_llvm_helper.cpp

@@ -28,6 +28,7 @@
 #include <llvm/IR/IRBuilder.h>
 #include <llvm/IR/LegacyPassManager.h>
 #include <llvm/Target/TargetMachine.h>
+#include <llvm/MC/MCSubtargetInfo.h>
 #include <llvm/Transforms/IPO.h>
 
 #include <cstring>
@@ -43,6 +44,12 @@
 #include "ac_llvm_build.h"
 #include "util/macros.h"
 
+bool ac_is_llvm_processor_supported(LLVMTargetMachineRef tm, const char *processor)
+{
+   llvm::TargetMachine *TM = reinterpret_cast<llvm::TargetMachine *>(tm);
+   return TM->getMCSubtargetInfo()->isCPUStringValid(processor);
+}
+
 void ac_add_attr_dereferenceable(LLVMValueRef val, uint64_t bytes)
 {
    llvm::Argument *A = llvm::unwrap<llvm::Argument>(val);

src/amd/llvm/ac_llvm_util.c

@@ -189,11 +189,18 @@ static LLVMTargetMachineRef ac_create_target_machine(enum radeon_family family,
    assert(family >= CHIP_TAHITI);
    const char *triple = (tm_options & AC_TM_SUPPORTS_SPILL) ? "amdgcn-mesa-mesa3d" : "amdgcn--";
    LLVMTargetRef target = ac_get_llvm_target(triple);
+   const char *name = ac_get_llvm_processor_name(family);
 
    LLVMTargetMachineRef tm =
-      LLVMCreateTargetMachine(target, triple, ac_get_llvm_processor_name(family), "", level,
+      LLVMCreateTargetMachine(target, triple, name, "", level,
                               LLVMRelocDefault, LLVMCodeModelDefault);
 
+   if (!ac_is_llvm_processor_supported(tm, name)) {
+      LLVMDisposeTargetMachine(tm);
+      fprintf(stderr, "amd: LLVM doesn't support %s, bailing out...\n", name);
+      return NULL;
+   }
+
    if (out_triple)
       *out_triple = triple;
 

src/amd/llvm/ac_llvm_util.h

@@ -90,6 +90,7 @@ struct ac_llvm_compiler {
 };
 
 const char *ac_get_llvm_processor_name(enum radeon_family family);
+bool ac_is_llvm_processor_supported(LLVMTargetMachineRef tm, const char *processor);
 void ac_add_attr_dereferenceable(LLVMValueRef val, uint64_t bytes);
 void ac_add_attr_alignment(LLVMValueRef val, uint64_t bytes);
 bool ac_is_sgpr_param(LLVMValueRef param);