Fix WavePrefixCountBits() being off by one.

It was counting bits up to the current lane included, whereas the documentation says it should be excluded. This now matches dxc's behavior as well. Fix KhronosGroup#2929
RPCS3 · Apr 22, 2022 · f906b89 · f906b89
1 parent 06ac141
commit f906b89
Show file tree

Hide file tree

Showing 2 changed files with 5 additions and 5 deletions.
diff --git a/Test/baseResults/hlsl.waveprefix.comp.out b/Test/baseResults/hlsl.waveprefix.comp.out
@@ -1126,7 +1126,7 @@ local_size = (32, 16, 1)
 0:54              0 (const int)
 0:54          Constant:
 0:54            0 (const int)
-0:54        subgroupBallotInclusiveBitCount ( temp uint)
+0:54        subgroupBallotExclusiveBitCount ( temp uint)
 0:54          subgroupBallot ( temp 4-component vector of uint)
 0:54            Compare Equal ( temp bool)
 0:54              direct index ( temp uint)
@@ -2289,7 +2289,7 @@ local_size = (32, 16, 1)
 0:54              0 (const int)
 0:54          Constant:
 0:54            0 (const int)
-0:54        subgroupBallotInclusiveBitCount ( temp uint)
+0:54        subgroupBallotExclusiveBitCount ( temp uint)
 0:54          subgroupBallot ( temp 4-component vector of uint)
 0:54            Compare Equal ( temp bool)
 0:54              direct index ( temp uint)
@@ -2818,7 +2818,7 @@ local_size = (32, 16, 1)
              390:      6(int) Load 389
              392:   391(bool) IEqual 390 26
              393:   13(ivec4) GroupNonUniformBallot 35 392
-             394:      6(int) GroupNonUniformBallotBitCount 35 InclusiveScan 393
+             394:      6(int) GroupNonUniformBallotBitCount 35 ExclusiveScan 393
              395:     42(ptr) AccessChain 24(data) 25 386 25 26
                               Store 395 394
                               Return

diff --git a/glslang/HLSL/hlslParseHelper.cpp b/glslang/HLSL/hlslParseHelper.cpp
@@ -5430,7 +5430,7 @@ void HlslParseContext::decomposeIntrinsic(const TSourceLoc& loc, TIntermTyped*&
         }
     case EOpWavePrefixCountBits:
         {
-            // Mapped to subgroupBallotInclusiveBitCount(subgroupBallot())
+            // Mapped to subgroupBallotExclusiveBitCount(subgroupBallot())
             // builtin
 
             // uvec4 type.
@@ -5444,7 +5444,7 @@ void HlslParseContext::decomposeIntrinsic(const TSourceLoc& loc, TIntermTyped*&
             TType uintType(EbtUint, EvqTemporary);
 
             node = intermediate.addBuiltInFunctionCall(loc,
-                EOpSubgroupBallotInclusiveBitCount, true, res, uintType);
+                EOpSubgroupBallotExclusiveBitCount, true, res, uintType);
 
             break;
         }