ac/llvm: add missing optimization barrier for 64-bit readlanes

Otherwise, LLVM optimizes it but it's actually incorrect.

Fixes: 0f45d4dc2b1 ("ac: add ac_build_readlane without optimization barrier")
Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3585>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3585>
(cherry picked from commit cc320ef9af6b84b6a1f275261b071d05c0ee6a62)

2 files changed, 41 insertions, 28 deletions

diff --git a/.pick_status.json b/.pick_status.json
index 2072a4b5d9a..ba880dae2be 100644
--- a/.pick_status.json
+++ b/.pick_status.json
@@ -607,7 +607,7 @@
         "description": "ac/llvm: add missing optimization barrier for 64-bit readlanes",
         "nominated": true,
         "nomination_type": 1,
-        "resolution": 0,
+        "resolution": 1,
         "master_sha": null,
         "because_sha": "0f45d4dc2b15e137346e1e3f064a24302e1c9048"
     },
diff --git a/src/amd/llvm/ac_llvm_build.c b/src/amd/llvm/ac_llvm_build.c
index a131c2a10cd..a1a9a453e4e 100644
--- a/src/amd/llvm/ac_llvm_build.c
+++ b/src/amd/llvm/ac_llvm_build.c
@@ -3611,11 +3611,15 @@ void ac_apply_fmask_to_sample(struct ac_llvm_context *ac, LLVMValueRef fmask,
 }
 
 static LLVMValueRef
-_ac_build_readlane(struct ac_llvm_context *ctx, LLVMValueRef src, LLVMValueRef lane)
+_ac_build_readlane(struct ac_llvm_context *ctx, LLVMValueRef src,
+		  LLVMValueRef lane, bool with_opt_barrier)
 {
 	LLVMTypeRef type = LLVMTypeOf(src);
 	LLVMValueRef result;
 
+	if (with_opt_barrier)
+		ac_build_optimization_barrier(ctx, &src);
+
 	src = LLVMBuildZExt(ctx->builder, src, ctx->i32, "");
 	if (lane)
 		lane = LLVMBuildZExt(ctx->builder, lane, ctx->i32, "");
@@ -3630,20 +3634,13 @@ _ac_build_readlane(struct ac_llvm_context *ctx, LLVMValueRef src, LLVMValueRef l
 	return LLVMBuildTrunc(ctx->builder, result, type, "");
 }
 
-/**
- * Builds the "llvm.amdgcn.readlane" or "llvm.amdgcn.readfirstlane" intrinsic.
- *
- * The optimization barrier is not needed if the value is the same in all lanes
- * or if this is called in the outermost block.
- *
- * @param ctx
- * @param src
- * @param lane - id of the lane or NULL for the first active lane
- * @return value of the lane
- */
-LLVMValueRef ac_build_readlane_no_opt_barrier(struct ac_llvm_context *ctx,
-					      LLVMValueRef src, LLVMValueRef lane)
+static LLVMValueRef
+ac_build_readlane_common(struct ac_llvm_context *ctx,
+			 LLVMValueRef src, LLVMValueRef lane,
+			 bool with_opt_barrier)
 {
+	LLVMTypeRef src_type = LLVMTypeOf(src);
+	src = ac_to_integer(ctx, src);
 	unsigned bits = LLVMGetIntTypeWidth(LLVMTypeOf(src));
 	LLVMValueRef ret;
 
@@ -3654,32 +3651,48 @@ LLVMValueRef ac_build_readlane_no_opt_barrier(struct ac_llvm_context *ctx,
 			LLVMBuildBitCast(ctx->builder, src, vec_type, "");
 		ret = LLVMGetUndef(vec_type);
 		for (unsigned i = 0; i < bits / 32; i++) {
+			LLVMValueRef ret_comp;
+
 			src = LLVMBuildExtractElement(ctx->builder, src_vector,
 						LLVMConstInt(ctx->i32, i, 0), "");
-			LLVMValueRef ret_comp = _ac_build_readlane(ctx, src, lane);
+
+			ret_comp = _ac_build_readlane(ctx, src, lane,
+						      with_opt_barrier);
+
 			ret = LLVMBuildInsertElement(ctx->builder, ret, ret_comp,
 						LLVMConstInt(ctx->i32, i, 0), "");
 		}
 	} else {
-		ret = _ac_build_readlane(ctx, src, lane);
+		ret = _ac_build_readlane(ctx, src, lane, with_opt_barrier);
 	}
 
-	return ret;
+	if (LLVMGetTypeKind(src_type) == LLVMPointerTypeKind)
+		return LLVMBuildIntToPtr(ctx->builder, ret, src_type, "");
+	return LLVMBuildBitCast(ctx->builder, ret, src_type, "");
 }
 
-LLVMValueRef
-ac_build_readlane(struct ac_llvm_context *ctx, LLVMValueRef src, LLVMValueRef lane)
+/**
+ * Builds the "llvm.amdgcn.readlane" or "llvm.amdgcn.readfirstlane" intrinsic.
+ *
+ * The optimization barrier is not needed if the value is the same in all lanes
+ * or if this is called in the outermost block.
+ *
+ * @param ctx
+ * @param src
+ * @param lane - id of the lane or NULL for the first active lane
+ * @return value of the lane
+ */
+LLVMValueRef ac_build_readlane_no_opt_barrier(struct ac_llvm_context *ctx,
+                                             LLVMValueRef src, LLVMValueRef lane)
 {
-	LLVMTypeRef src_type = LLVMTypeOf(src);
-	src = ac_to_integer(ctx, src);
-	LLVMValueRef ret;
+	return ac_build_readlane_common(ctx, src, lane, false);
+}
 
-	ac_build_optimization_barrier(ctx, &src);
 
-	ret = ac_build_readlane_no_opt_barrier(ctx, src, lane);
-	if (LLVMGetTypeKind(src_type) == LLVMPointerTypeKind)
-		return LLVMBuildIntToPtr(ctx->builder, ret, src_type, "");
-	return LLVMBuildBitCast(ctx->builder, ret, src_type, "");
+LLVMValueRef
+ac_build_readlane(struct ac_llvm_context *ctx, LLVMValueRef src, LLVMValueRef lane)
+{
+	return ac_build_readlane_common(ctx, src, lane, true);
 }
 
 LLVMValueRef