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For some context about why it's needed see
https://github.com/compiler-explorer/compiler-explorer/pull/5373#issuecomment-1687127788
The short version is that currently CUDA compilation is broken w/ clang with
unpatched libstdc++. Ubuntu and Debian patch libstdc++ to avoid the problem,
but this should be handled by clang.
GPUs do not have actual FP128 support, but we do need to be able to compile
host-side headers which use `__float128`. On the GPU side we'll downgrade
`__float128`
to double, similarly to how we handle `long double`. Both types will have
different in-memory representation compared to their host counterparts and are
not expected to be interchangeable across host/device boundary.
Also see https://reviews.llvm.org/D78513 which applied equivalent change to
HIP/AMDGPU.
Repository:
rG LLVM Github Monorepo
https://reviews.llvm.org/D158778
Files:
clang/lib/Basic/Targets/NVPTX.cpp
clang/test/SemaCUDA/amdgpu-f128.cu
clang/test/SemaCUDA/f128.cu
Index: clang/test/SemaCUDA/f128.cu
===================================================================
--- clang/test/SemaCUDA/f128.cu
+++ clang/test/SemaCUDA/f128.cu
@@ -1,4 +1,5 @@
// RUN: %clang_cc1 -triple amdgcn-amd-amdhsa -aux-triple
x86_64-unknown-linux-gnu -fcuda-is-device -fsyntax-only -verify %s
+// RUN: %clang_cc1 -triple nvptx64 -aux-triple x86_64-unknown-linux-gnu
-fcuda-is-device -fsyntax-only -verify %s
// expected-no-diagnostics
typedef __float128 f128_t;
Index: clang/lib/Basic/Targets/NVPTX.cpp
===================================================================
--- clang/lib/Basic/Targets/NVPTX.cpp
+++ clang/lib/Basic/Targets/NVPTX.cpp
@@ -142,6 +142,20 @@
// we need all classes to be defined on both the host and device.
MaxAtomicInlineWidth = HostTarget->getMaxAtomicInlineWidth();
+ // For certain builtin types support on the host target, claim they are
+ // support to pass the compilation of the host code during the device-side
+ // compilation.
+ //
+ // FIXME: As the side effect, we also accept `__float128` uses in the device
+ // code, but use 'double' as the underlying type, so host/device
+ // representation of the type is different. This is similar to what happens
to
+ // long double.
+
+ if (HostTarget->hasFloat128Type()) {
+ HasFloat128 = true;
+ Float128Format = DoubleFormat;
+ }
+
// Properties intentionally not copied from host:
// - LargeArrayMinWidth, LargeArrayAlign: Not visible across the
// host/device boundary.
Index: clang/test/SemaCUDA/f128.cu
===================================================================
--- clang/test/SemaCUDA/f128.cu
+++ clang/test/SemaCUDA/f128.cu
@@ -1,4 +1,5 @@
// RUN: %clang_cc1 -triple amdgcn-amd-amdhsa -aux-triple x86_64-unknown-linux-gnu -fcuda-is-device -fsyntax-only -verify %s
+// RUN: %clang_cc1 -triple nvptx64 -aux-triple x86_64-unknown-linux-gnu -fcuda-is-device -fsyntax-only -verify %s
// expected-no-diagnostics
typedef __float128 f128_t;
Index: clang/lib/Basic/Targets/NVPTX.cpp
===================================================================
--- clang/lib/Basic/Targets/NVPTX.cpp
+++ clang/lib/Basic/Targets/NVPTX.cpp
@@ -142,6 +142,20 @@
// we need all classes to be defined on both the host and device.
MaxAtomicInlineWidth = HostTarget->getMaxAtomicInlineWidth();
+ // For certain builtin types support on the host target, claim they are
+ // support to pass the compilation of the host code during the device-side
+ // compilation.
+ //
+ // FIXME: As the side effect, we also accept `__float128` uses in the device
+ // code, but use 'double' as the underlying type, so host/device
+ // representation of the type is different. This is similar to what happens to
+ // long double.
+
+ if (HostTarget->hasFloat128Type()) {
+ HasFloat128 = true;
+ Float128Format = DoubleFormat;
+ }
+
// Properties intentionally not copied from host:
// - LargeArrayMinWidth, LargeArrayAlign: Not visible across the
// host/device boundary.
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