From 6af960cef28c608a9be7c2b350969a5416e610a6 Mon Sep 17 00:00:00 2001
From: Bill Currie <bill@taniwha.org>
Date: Mon, 17 Feb 2025 20:58:45 +0900
Subject: [PATCH] [qfcc] Implement `discard`

I had no idea how to do it back when I started working on the glsl
parser, but intrinsics made it very easy. It's just OpKill for now (and
might stay that way for glsl).
---
 tools/qfcc/source/glsl-builtins.c | 1 +
 tools/qfcc/source/glsl-parse.y    | 6 +++++-
 tools/qfcc/source/target_spirv.c  | 3 ++-
 3 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/tools/qfcc/source/glsl-builtins.c b/tools/qfcc/source/glsl-builtins.c
index 0d20b55da..f126b52f2 100644
--- a/tools/qfcc/source/glsl-builtins.c
+++ b/tools/qfcc/source/glsl-builtins.c
@@ -1128,6 +1128,7 @@ SRC_LINE
 //fragment processing functions
 static const char *glsl_fragment_functions =
 SRC_LINE
+"void __discard() = " SPV(OpKill) ";"                                   "\n"
 "@generic(genFType=@vector(float)) {"                                   "\n"
 "genFType dFdx(genFType p) = " SPV(OpDPdx) ";"                          "\n"
 "genFType dFdy(genFType p) = " SPV(OpDPdy) ";"                          "\n"
diff --git a/tools/qfcc/source/glsl-parse.y b/tools/qfcc/source/glsl-parse.y
index 2d178ab04..7799b3796 100644
--- a/tools/qfcc/source/glsl-parse.y
+++ b/tools/qfcc/source/glsl-parse.y
@@ -1326,7 +1326,11 @@ jump_statement
 		}
 	| RETURN ';'				{ $$ = new_return_expr (nullptr); }
 	| RETURN expression ';'		{ $$ = new_return_expr ($2); }
-	| DISCARD ';'				{ $$ = nullptr; } //XXX
+	| DISCARD ';'
+		{
+			auto func = new_name_expr ("__discard");
+			$$ = new_call_expr (func, nullptr, nullptr);
+		}
 	;
 
 %%
diff --git a/tools/qfcc/source/target_spirv.c b/tools/qfcc/source/target_spirv.c
index c9db14731..c4ec7e2a9 100644
--- a/tools/qfcc/source/target_spirv.c
+++ b/tools/qfcc/source/target_spirv.c
@@ -129,7 +129,8 @@ is_block_terminated (defspace_t *code_space)
 			|| (INSN(last_insn, 0) & SpvOpCodeMask) == SpvOpReturnValue
 			|| (INSN(last_insn, 0) & SpvOpCodeMask) == SpvOpUnreachable
 			|| (INSN(last_insn, 0) & SpvOpCodeMask) == SpvOpBranchConditional
-			|| (INSN(last_insn, 0) & SpvOpCodeMask) == SpvOpBranch)) {
+			|| (INSN(last_insn, 0) & SpvOpCodeMask) == SpvOpBranch
+			|| (INSN(last_insn, 0) & SpvOpCodeMask) == SpvOpKill)) {
 		return true;
 	}
 	return false;