From 0000916e7552b8d6fed91ffa8c77920913272e9d Mon Sep 17 00:00:00 2001
From: baldurk <baldurk@baldurk.org>
Date: Tue, 9 Jun 2020 12:16:16 +0100
Subject: [PATCH] Expose svbr rotated encoding as static member of LLVM bit
 reader

---
 .../driver/shaders/dxil/dxil_bytecode.cpp     |  6 +-----
 .../driver/shaders/dxil/llvm_bitreader.h      | 15 +++-----------
 .../driver/shaders/dxil/llvm_decoder.cpp      | 20 +++++++++----------
 3 files changed, 14 insertions(+), 27 deletions(-)

diff --git a/renderdoc/driver/shaders/dxil/dxil_bytecode.cpp b/renderdoc/driver/shaders/dxil/dxil_bytecode.cpp
index 655bd9e54..f97691245 100644
--- a/renderdoc/driver/shaders/dxil/dxil_bytecode.cpp
+++ b/renderdoc/driver/shaders/dxil/dxil_bytecode.cpp
@@ -243,11 +243,7 @@ void ParseConstant(const LLVMBC::BlockOrRecord &constant, const Type *&curType,
   {
     Value v;
     v.type = curType;
-    v.val.u64v[0] = constant.ops[0];
-    if(v.val.u64v[0] & 0x1)
-      v.val.s64v[0] = -int64_t(v.val.u64v[0] >> 1);
-    else
-      v.val.u64v[0] >>= 1;
+    v.val.s64v[0] = LLVMBC::BitReader::svbr(constant.ops[0]);
     addValue(v);
   }
   else if(IS_KNOWN(constant.id, ConstantsRecord::FLOAT))
diff --git a/renderdoc/driver/shaders/dxil/llvm_bitreader.h b/renderdoc/driver/shaders/dxil/llvm_bitreader.h
index 1735bf9fa..b46589178 100644
--- a/renderdoc/driver/shaders/dxil/llvm_bitreader.h
+++ b/renderdoc/driver/shaders/dxil/llvm_bitreader.h
@@ -116,22 +116,13 @@ public:
     return T(ret);
   }
 
-  template <typename T>
-  T svbr(size_t groupBitSize)
+  static int64_t svbr(uint64_t var)
   {
-    // the value will fit in a uint64_t because the any negative values with the high bit set, which
-    // would overflow when shifted, no longer have the high bit set after being negated.
-    uint64_t var = vbr<uint64_t>(groupBitSize);
-
     // if the low bit is set, it's negative
     if(var & 0x1)
-    {
-      return T(-int64_t(var >> 1));
-    }
+      return -int64_t(var >> 1);
     else
-    {
-      return T(var >> 1);
-    }
+      return int64_t(var >> 1);
   }
 
   template <typename T>
diff --git a/renderdoc/driver/shaders/dxil/llvm_decoder.cpp b/renderdoc/driver/shaders/dxil/llvm_decoder.cpp
index 9fdb56e7c..ac6579d6a 100644
--- a/renderdoc/driver/shaders/dxil/llvm_decoder.cpp
+++ b/renderdoc/driver/shaders/dxil/llvm_decoder.cpp
@@ -759,34 +759,34 @@ TEST_CASE("Check LLVM bitreader", "[llvm]")
 
       int64_t val;
 
-      val = b.svbr<int64_t>(4);
+      val = LLVMBC::BitReader::svbr(b.vbr<uint64_t>(4));
       CHECK(val == 2);
 
-      val = b.svbr<int64_t>(4);
+      val = LLVMBC::BitReader::svbr(b.vbr<uint64_t>(4));
       CHECK(val == 0);
 
-      val = b.svbr<int64_t>(4);
+      val = LLVMBC::BitReader::svbr(b.vbr<uint64_t>(4));
       CHECK(val == -2);
 
-      val = b.svbr<int64_t>(4);
+      val = LLVMBC::BitReader::svbr(b.vbr<uint64_t>(4));
       CHECK(val == 0);
 
-      val = b.svbr<int64_t>(4);
+      val = LLVMBC::BitReader::svbr(b.vbr<uint64_t>(4));
       CHECK(val == 98765);
 
-      val = b.svbr<int64_t>(4);
+      val = LLVMBC::BitReader::svbr(b.vbr<uint64_t>(4));
       CHECK(val == -98765);
 
-      val = b.svbr<int64_t>(4);
+      val = LLVMBC::BitReader::svbr(b.vbr<uint64_t>(4));
       CHECK(val == INT64_MAX);
 
-      val = b.svbr<int64_t>(4);
+      val = LLVMBC::BitReader::svbr(b.vbr<uint64_t>(4));
       CHECK(val == -INT64_MAX);
 
-      val = b.svbr<int64_t>(4);
+      val = LLVMBC::BitReader::svbr(b.vbr<uint64_t>(4));
       CHECK(val == 3);
 
-      val = b.svbr<int64_t>(4);
+      val = LLVMBC::BitReader::svbr(b.vbr<uint64_t>(4));
       CHECK(val == 0);
 
       // should be exactly at the end of the stream