From 73bb454f66a07a654e88a9f4511f37fc0be9ed29 Mon Sep 17 00:00:00 2001
From: Rex Xu <rex.xu@amd.com>
Date: Wed, 8 Nov 2023 15:37:44 +0800
Subject: [PATCH] Fix issues of fract(x)
The problem is similar to modf(x) when x=-0.0 or +INF/-INF. Although
SPIR-V spec says nothing about such cases, the OpenCL spec does define
the results of those operations as follow:
fract(-0.0) = -0.0
fract(+INF) = 0.0
fract(-INF) = -0.0
Hence, we follow what have been done for modf.
---
lgc/include/lgc/state/IntrinsDefs.h | 14 ---------
lgc/interface/lgc/Builder.h | 14 +++++++++
llpc/translator/lib/SPIRV/SPIRVReader.cpp | 37 +++++++++++++++++++++--
3 files changed, 49 insertions(+), 16 deletions(-)
diff --git a/lgc/include/lgc/state/IntrinsDefs.h b/lgc/include/lgc/state/IntrinsDefs.h
index f025fec45b..05b2920fba 100644
--- a/lgc/include/lgc/state/IntrinsDefs.h
+++ b/lgc/include/lgc/state/IntrinsDefs.h
@@ -466,20 +466,6 @@ enum BufDstSel {
BUF_DST_SEL_W = 7, // SEL_W (W)
};
-// Bits in mask supplied to v_cmp_class
-enum CmpClass {
- SignalingNaN = 1,
- QuietNaN = 2,
- NegativeInfinity = 4,
- NegativeNormal = 8,
- NegativeSubnormal = 0x10,
- NegativeZero = 0x20,
- PositiveZero = 0x40,
- PositiveSubnormal = 0x80,
- PositiveNormal = 0x100,
- PositiveInfinity = 0x200
-};
-
// Represents register fields of SPI_PS_INPUT_ADDR.
union SpiPsInputAddr {
struct {
diff --git a/lgc/interface/lgc/Builder.h b/lgc/interface/lgc/Builder.h
index b8a64f1b51..4639ed4a7e 100644
--- a/lgc/interface/lgc/Builder.h
+++ b/lgc/interface/lgc/Builder.h
@@ -345,6 +345,20 @@ class BuilderDefs : public BuilderCommon {
ImageAtomicFMax = 12, // Atomic operation: fmax
ImageAtomicFAdd = 13 // Atomic operation: fadd
};
+
+ // Bits in mask supplied to createIsFPClass
+ enum CmpClass {
+ SignalingNaN = 1,
+ QuietNaN = 2,
+ NegativeInfinity = 4,
+ NegativeNormal = 8,
+ NegativeSubnormal = 0x10,
+ NegativeZero = 0x20,
+ PositiveZero = 0x40,
+ PositiveSubnormal = 0x80,
+ PositiveNormal = 0x100,
+ PositiveInfinity = 0x200
+ };
};
// =====================================================================================================================
diff --git a/llpc/translator/lib/SPIRV/SPIRVReader.cpp b/llpc/translator/lib/SPIRV/SPIRVReader.cpp
index 6d677c897a..8011085926 100644
--- a/llpc/translator/lib/SPIRV/SPIRVReader.cpp
+++ b/llpc/translator/lib/SPIRV/SPIRVReader.cpp
@@ -8808,9 +8808,42 @@ Value *SPIRVToLLVM::transGLSLExtInst(SPIRVExtInst *extInst, BasicBlock *bb) {
// Round up to whole number
return getBuilder()->CreateUnaryIntrinsic(Intrinsic::ceil, args[0]);
- case GLSLstd450Fract:
+ case GLSLstd450Fract: {
// Get fractional part
- return getBuilder()->CreateFract(args[0]);
+ auto fract = getBuilder()->CreateFract(args[0]);
+
+ // NOTE: Although SPIR-V spec says nothing about such cases: fract(-0.0), fract(+INF), fract(-INF), OpenCL spec does
+ // have following definitions:
+ //
+ // fract(-0.0) = -0.0
+ // fract(+INF) = +0.0
+ // fract(-INF) = -0.0
+ //
+ // When we follow it, we have two issues that are similar to modf(x):
+ //
+ // 1. When we input x=+INF/-INF to above formula, we finally get the computation of (-INF) + INF or INF - INF.
+ // The result is NaN returned by HW.
+ // 2. When we input x=-0.0 to above formula, we finally get the addition of (-0.0) + 0.0. The result is +0.0
+ // returned by HW.
+ //
+ // Hence, we have to manually check those special cases:
+ //
+ // y = fract(x)
+ // y = x == -0.0 || x == INF ? copysign(0.0, x) : y, when either NSZ or NoInfs is not present
+ unsigned checkFlags = 0;
+ if (!getBuilder()->getFastMathFlags().noSignedZeros())
+ checkFlags |= lgc::Builder::CmpClass::NegativeZero;
+ if (!getBuilder()->getFastMathFlags().noInfs())
+ checkFlags |= (lgc::Builder::CmpClass::NegativeZero | lgc::Builder::CmpClass::NegativeZero);
+
+ if (checkFlags) {
+ Value *isNegZeroOrInf = getBuilder()->createIsFPClass(args[0], checkFlags);
+ Value *signedZero = getBuilder()->CreateCopySign(ConstantFP::getNullValue(args[0]->getType()), args[0]);
+ fract = getBuilder()->CreateSelect(isNegZeroOrInf, signedZero, fract);
+ }
+
+ return fract;
+ }
case GLSLstd450Radians:
// Convert from degrees to radians