radeonsi: add a debug flag for unsafe math LLVM optimizations

Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>

src/gallium/drivers/radeon/r600_pipe_common.c

@@ -482,6 +482,7 @@ static const struct debug_named_value common_debug_options[] = {
 	{ "sisched", DBG_SI_SCHED, "Enable LLVM SI Machine Instruction Scheduler." },
 	{ "mono", DBG_MONOLITHIC_SHADERS, "Use old-style monolithic shaders compiled on demand" },
 	{ "noce", DBG_NO_CE, "Disable the constant engine"},
+	{ "unsafemath", DBG_UNSAFE_MATH, "Enable unsafe math shader optimizations" },
 
 	DEBUG_NAMED_VALUE_END /* must be last */
 };

src/gallium/drivers/radeon/r600_pipe_common.h

@@ -99,6 +99,7 @@
 #define DBG_SI_SCHED		(1llu << 46)
 #define DBG_MONOLITHIC_SHADERS	(1llu << 47)
 #define DBG_NO_CE		(1llu << 48)
+#define DBG_UNSAFE_MATH		(1llu << 49)
 
 #define R600_MAP_BUFFER_ALIGNMENT 64
 #define R600_MAX_VIEWPORTS        16

src/gallium/drivers/radeonsi/si_shader.c

@@ -5255,6 +5255,22 @@ static void si_create_function(struct si_shader_context *ctx,
 		else
 			LLVMAddAttribute(P, LLVMInRegAttribute);
 	}
+
+	if (ctx->screen->b.debug_flags & DBG_UNSAFE_MATH) {
+		/* These were copied from some LLVM test. */
+		LLVMAddTargetDependentFunctionAttr(ctx->radeon_bld.main_fn,
+						   "less-precise-fpmad",
+						   "true");
+		LLVMAddTargetDependentFunctionAttr(ctx->radeon_bld.main_fn,
+						   "no-infs-fp-math",
+						   "true");
+		LLVMAddTargetDependentFunctionAttr(ctx->radeon_bld.main_fn,
+						   "no-nans-fp-math",
+						   "true");
+		LLVMAddTargetDependentFunctionAttr(ctx->radeon_bld.main_fn,
+						   "unsafe-fp-math",
+						   "true");
+	}
 }
 
 static void create_meta_data(struct si_shader_context *ctx)