From: Marek Olšák <marek.olsak@amd.com>
Date: Sat, 25 Aug 2018 03:00:37 +0000 (-0400)
Subject: ac: revert new LLVM 7.0 behavior for fdiv
X-Git-Url: https://git.libre-soc.org/?a=commitdiff_plain;h=a5f35aa742c3f1e2fae6a6c2fb53f92822f0cb70;p=mesa.git

ac: revert new LLVM 7.0 behavior for fdiv

Cc: 18.2 <mesa-stable@lists.freedesktop.org>
Tested-by: Dieter Nützel <Dieter@nuetzel-hh.de>
---

diff --git a/src/amd/common/ac_llvm_build.c b/src/amd/common/ac_llvm_build.c
index c741a1ab62d..629cd2a7527 100644
--- a/src/amd/common/ac_llvm_build.c
+++ b/src/amd/common/ac_llvm_build.c
@@ -561,7 +561,14 @@ ac_build_fdiv(struct ac_llvm_context *ctx,
 	      LLVMValueRef num,
 	      LLVMValueRef den)
 {
-	LLVMValueRef ret = LLVMBuildFDiv(ctx->builder, num, den, "");
+	/* If we do (num / den), LLVM >= 7.0 does:
+	 *    return num * v_rcp_f32(den * (fabs(den) > 0x1.0p+96f ? 0x1.0p-32f : 1.0f));
+	 *
+	 * If we do (num * (1 / den)), LLVM does:
+	 *    return num * v_rcp_f32(den);
+	 */
+	LLVMValueRef rcp = LLVMBuildFDiv(ctx->builder, ctx->f32_1, den, "");
+	LLVMValueRef ret = LLVMBuildFMul(ctx->builder, num, rcp, "");
 
 	/* Use v_rcp_f32 instead of precise division. */
 	if (!LLVMIsConstant(ret))