radeonsi: Add debug option to enable LLVM GlobalISel (v2)

R600_DEBUG=gisel will tell LLVM to use GlobalISel rather than
SelectionDAG for instruction selection.

v2: mareko: move the helper to src/amd/common

Signed-off-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Tom Stellard <tstellar@redhat.com>

src/amd/common/ac_llvm_helper.cpp

@@ -171,3 +171,10 @@ void ac_llvm_add_barrier_noop_pass(LLVMPassManagerRef passmgr)
 {
 	llvm::unwrap(passmgr)->add(llvm::createBarrierNoopPass());
 }
+
+void ac_enable_global_isel(LLVMTargetMachineRef tm)
+{
+#if HAVE_LLVM >= 0x0700
+  reinterpret_cast<llvm::TargetMachine*>(tm)->setGlobalISel(true);
+#endif
+}

src/amd/common/ac_llvm_util.c

@@ -34,6 +34,7 @@
 #include <llvm-c/Transforms/Utils.h>
 #endif
 #include "c11/threads.h"
+#include "gallivm/lp_bld_misc.h"
 #include "util/u_math.h"
 
 #include <assert.h>
@@ -55,9 +56,13 @@ static void ac_init_llvm_target()
 	 * https://reviews.llvm.org/D26348
 	 *
 	 * "mesa" is the prefix for error messages.
+	 *
+	 * -global-isel-abort=2 is a no-op unless global isel has been enabled.
+	 * This option tells the backend to fall-back to SelectionDAG and print
+	 * a diagnostic message if global isel fails.
 	 */
-	const char *argv[2] = { "mesa", "-simplifycfg-sink-common=false" };
+	const char *argv[3] = { "mesa", "-simplifycfg-sink-common=false", "-global-isel-abort=2" };
-	LLVMParseCommandLineOptions(2, argv, NULL);
+	LLVMParseCommandLineOptions(3, argv, NULL);
 }
 
 static once_flag ac_init_llvm_target_once_flag = ONCE_FLAG_INIT;
@@ -164,6 +169,8 @@ static LLVMTargetMachineRef ac_create_target_machine(enum radeon_family family,
 
 	if (out_triple)
 		*out_triple = triple;
+	if (tm_options & AC_TM_ENABLE_GLOBAL_ISEL)
+		ac_enable_global_isel(tm);
 	return tm;
 }
 

src/amd/common/ac_llvm_util.h

@@ -63,6 +63,7 @@ enum ac_target_machine_options {
 	AC_TM_FORCE_DISABLE_XNACK = (1 << 3),
 	AC_TM_PROMOTE_ALLOCA_TO_SCRATCH = (1 << 4),
 	AC_TM_CHECK_IR = (1 << 5),
+	AC_TM_ENABLE_GLOBAL_ISEL = (1 << 6),
 };
 
 enum ac_float_mode {
@@ -134,6 +135,7 @@ void ac_destroy_llvm_passes(struct ac_compiler_passes *p);
 bool ac_compile_module_to_binary(struct ac_compiler_passes *p, LLVMModuleRef module,
 				 struct ac_shader_binary *binary);
 void ac_llvm_add_barrier_noop_pass(LLVMPassManagerRef passmgr);
+void ac_enable_global_isel(LLVMTargetMachineRef tm);
 
 #ifdef __cplusplus
 }

src/gallium/drivers/radeonsi/si_pipe.c

@@ -57,6 +57,7 @@ static const struct debug_named_value debug_options[] = {
 	/* Shader compiler options the shader cache should be aware of: */
 	{ "unsafemath", DBG(UNSAFE_MATH), "Enable unsafe math shader optimizations" },
 	{ "sisched", DBG(SI_SCHED), "Enable LLVM SI Machine Instruction Scheduler." },
+	{ "gisel", DBG(GISEL), "Enable LLVM global instruction selector." },
 
 	/* Shader compiler options (with no effect on the shader cache): */
 	{ "checkir", DBG(CHECK_IR), "Enable additional sanity checks on shader IR" },
@@ -109,6 +110,7 @@ static void si_init_compiler(struct si_screen *sscreen,
 {
 	enum ac_target_machine_options tm_options =
 		(sscreen->debug_flags & DBG(SI_SCHED) ? AC_TM_SISCHED : 0) |
+		(sscreen->debug_flags & DBG(GISEL) ? AC_TM_ENABLE_GLOBAL_ISEL : 0) |
 		(sscreen->info.chip_class >= GFX9 ? AC_TM_FORCE_ENABLE_XNACK : 0) |
 		(sscreen->info.chip_class < GFX9 ? AC_TM_FORCE_DISABLE_XNACK : 0) |
 		(!sscreen->llvm_has_working_vgpr_indexing ? AC_TM_PROMOTE_ALLOCA_TO_SCRATCH : 0) |
@@ -756,6 +758,7 @@ static void si_disk_cache_create(struct si_screen *sscreen)
 			/* These flags affect shader compilation. */
 			#define ALL_FLAGS (DBG(FS_CORRECT_DERIVS_AFTER_KILL) | \
 					   DBG(SI_SCHED) | \
+					   DBG(GISEL) | \
 					   DBG(UNSAFE_MATH) | \
 					   DBG(NIR))
 			uint64_t shader_debug_flags = sscreen->debug_flags &

src/gallium/drivers/radeonsi/si_pipe.h

@@ -121,6 +121,7 @@ enum {
 	DBG_FS_CORRECT_DERIVS_AFTER_KILL,
 	DBG_UNSAFE_MATH,
 	DBG_SI_SCHED,
+	DBG_GISEL,
 
 	/* Shader compiler options (with no effect on the shader cache): */
 	DBG_CHECK_IR,