clang/AMDGPU: Assume denormals are enabled for the default target.

[arsenm]

Summary

Since the default logic was based on having fast denormal/fma
features, and the default target has no features, we assumed flushing by
default. This fixes incorrectly assuming flushing in builds for
"generic" IR libraries.

The handling for no specified --cuda-gpu-arch in HIP is kind of
broken. Somewhere else forces a default target of gfx803, which does
not enable denormal handling by default. We don't see this default
switching here, so you'll end up with a different denormal mode
depending on whether you explicitly requested gfx803, or used it by
default.

[yaxunl]

I think https://reviews.llvm.org/D78019 should fix the issue about HIP not using correct default denormal value if no arch is specified.

In that case, driver actually sets offloading arch to gfx803 and clang should be able to see it in JobAction.

[arsenm]

In D78020#1978034, @yaxunl wrote:

I think https://reviews.llvm.org/D78019 should fix the issue about HIP not using correct default denormal value if no arch is specified.

In that case, driver actually sets offloading arch to gfx803 and clang should be able to see it in JobAction.

It doesn't, that patch is the parent of this one. This use an empty offloading arch and I wasn't sure where the codegen default was forced

[arsenm]

Fix test

[arsenm]

In D78020#1978034, @yaxunl wrote:

I think https://reviews.llvm.org/D78019 should fix the issue about HIP not using correct default denormal value if no arch is specified.

In that case, driver actually sets offloading arch to gfx803 and clang should be able to see it in JobAction.

I just tried again and you're right, the function does see the explicit GK_GFX803

[yaxunl]

clang/test/Driver/cuda-flush-denormals-to-zero.cu

26

this comment can be removed or modified

[arsenm]

Fix comment

[yaxunl]

LGTM. Thanks.

[arsenm]

3a612450508b314b7a6f4db142d0c619031d760e

clang/lib/Driver/ToolChains/AMDGPU.cpp

if (!Args.hasArg(options::OPT_O, options::OPT_O0, options::OPT_O4,
                         getOptionDefault(options::OPT_O));
   }
 
   return DAL;
 }
 
 bool AMDGPUToolChain::getDefaultDenormsAreZeroForTarget(
     llvm::AMDGPU::GPUKind Kind) {
+
+  // Assume nothing without a specific target.
+  if (Kind == llvm::AMDGPU::GK_NONE)
+    return false;
+
   const unsigned ArchAttr = llvm::AMDGPU::getArchAttrAMDGCN(Kind);
 
   // Default to enabling f32 denormals by default on subtargets where fma is
   // fast with denormals
   const bool BothDenormAndFMAFast =
       (ArchAttr & llvm::AMDGPU::FEATURE_FAST_FMA_F32) &&
       (ArchAttr & llvm::AMDGPU::FEATURE_FAST_DENORMAL_F32);
   return !BothDenormAndFMAFast;

clang/test/Driver/cl-denorms-are-zero.cl

 // Slow FMAF and slow f32 denormals
-// RUN: %clang -### -target amdgcn--amdhsa -c -mcpu=pitcairn %s 2>&1 | FileCheck -check-prefixes=AMDGCN,AMDGCN-FLUSH %s
+// RUN: %clang -### -target amdgcn--amdhsa -nogpulib -c -mcpu=pitcairn %s 2>&1 | FileCheck -check-prefixes=AMDGCN,AMDGCN-FLUSH %s
 // RUN: %clang -### -cl-denorms-are-zero -o - -target amdgcn--amdhsa -c -mcpu=pitcairn %s 2>&1 | FileCheck -check-prefixes=AMDGCN,AMDGCN-FLUSH %s
 
 // Fast FMAF, but slow f32 denormals
-// RUN: %clang -### -target amdgcn--amdhsa -c -mcpu=tahiti %s 2>&1 | FileCheck -check-prefixes=AMDGCN,AMDGCN-FLUSH %s
+// RUN: %clang -### -target amdgcn--amdhsa -nogpulib -c -mcpu=tahiti %s 2>&1 | FileCheck -check-prefixes=AMDGCN,AMDGCN-FLUSH %s
 // RUN: %clang -### -cl-denorms-are-zero -o - -target amdgcn--amdhsa -c -mcpu=tahiti %s 2>&1 | FileCheck -check-prefixes=AMDGCN,AMDGCN-FLUSH %s
 
 // Fast F32 denormals, but slow FMAF
-// RUN: %clang -### -target amdgcn--amdhsa -c -mcpu=fiji %s 2>&1 | FileCheck -check-prefixes=AMDGCN,AMDGCN-FLUSH %s
+// RUN: %clang -### -target amdgcn--amdhsa -nogpulib -c -mcpu=fiji %s 2>&1 | FileCheck -check-prefixes=AMDGCN,AMDGCN-FLUSH %s
 // RUN: %clang -### -cl-denorms-are-zero -o - -target amdgcn--amdhsa -c -mcpu=fiji %s 2>&1 | FileCheck -check-prefixes=AMDGCN,AMDGCN-FLUSH %s
 
 // Fast F32 denormals and fast FMAF
-// RUN: %clang -### -target amdgcn--amdhsa -c -mcpu=gfx900 %s 2>&1 | FileCheck -check-prefixes=AMDGCN,AMDGCN-DENORM %s
-// RUN: %clang -### -cl-denorms-are-zero -o - -target amdgcn--amdhsa -c -mcpu=gfx900 %s 2>&1 | FileCheck -check-prefixes=AMDGCN,AMDGCN-FLUSH %s
+// RUN: %clang -### -target amdgcn--amdhsa -nogpulib -c -mcpu=gfx900 %s 2>&1 | FileCheck -check-prefixes=AMDGCN,AMDGCN-DENORM %s
+// RUN: %clang -### -cl-denorms-are-zero -o - -target amdgcn--amdhsa -nogpulib -c -mcpu=gfx900 %s 2>&1 | FileCheck -check-prefixes=AMDGCN,AMDGCN-FLUSH %s
+
+// Default target is artificial, but should assume a conservative default.
+// RUN: %clang -### -target amdgcn--amdhsa -nogpulib -c %s 2>&1 | FileCheck -check-prefixes=AMDGCN,AMDGCN-DENORM %s
+// RUN: %clang -### -cl-denorms-are-zero -o - -target amdgcn--amdhsa -nogpulib -c %s 2>&1 | FileCheck -check-prefixes=AMDGCN,AMDGCN-FLUSH %s
 
 // AMDGCN-FLUSH: "-fdenormal-fp-math-f32=preserve-sign,preserve-sign"
 
 // This should be omitted and default to ieee
-// AMDGCN-DENORM-NOT: "-fdenormal-fp-math-f32"
+// AMDGCN-DENORM-NOT: denormal-fp-math

clang/test/Driver/cuda-flush-denormals-to-zero.cu

 
 // RUN: %clang -x hip -no-canonical-prefixes -### -target x86_64-linux-gnu -c -march=haswell --cuda-gpu-arch=gfx900 -fcuda-flush-denormals-to-zero -nocudainc -nogpulib %s 2>&1 | FileCheck -check-prefix=FTZ %s
 // RUN: %clang -x hip -no-canonical-prefixes -### -target x86_64-linux-gnu -c -march=haswell --cuda-gpu-arch=gfx900 -fno-cuda-flush-denormals-to-zero -nocudainc -nogpulib %s 2>&1 | FileCheck -check-prefix=NOFTZ %s
 
 // Test the default changing with no argument based on the subtarget in HIP mode
 // RUN: %clang -x hip -no-canonical-prefixes -### -target x86_64-linux-gnu -c -march=haswell --cuda-gpu-arch=gfx803 -nocudainc -nogpulib %s 2>&1 | FileCheck -check-prefix=FTZ %s
 // RUN: %clang -x hip -no-canonical-prefixes -### -target x86_64-linux-gnu -c -march=haswell --cuda-gpu-arch=gfx900 -nocudainc -nogpulib %s 2>&1 | FileCheck -check-prefix=NOFTZ %s
 
+// Test no subtarget, which should get the denormal setting of the default gfx803
+// RUN: %clang -x hip -no-canonical-prefixes -### -target x86_64-linux-gnu -c -march=haswell -nocudainc -nogpulib %s 2>&1 | FileCheck -check-prefix=FTZ %s
 
 // Test multiple offload archs with different defaults.
 // RUN: %clang -x hip -no-canonical-prefixes -### -target x86_64-linux-gnu -c -march=haswell --cuda-gpu-arch=gfx803 --cuda-gpu-arch=gfx900 -nocudainc -nogpulib %s 2>&1 | FileCheck -check-prefix=MIXED-DEFAULT-MODE %s
 // RUN: %clang -x hip -no-canonical-prefixes -### -target x86_64-linux-gnu -c -march=haswell -fcuda-flush-denormals-to-zero --cuda-gpu-arch=gfx803 --cuda-gpu-arch=gfx900 -nocudainc -nogpulib %s 2>&1 | FileCheck -check-prefix=FTZX2 %s
 // RUN: %clang -x hip -no-canonical-prefixes -### -target x86_64-linux-gnu -c -march=haswell -fno-cuda-flush-denormals-to-zero --cuda-gpu-arch=gfx803 --cuda-gpu-arch=gfx900 -nocudainc -nogpulib %s 2>&1 | FileCheck -check-prefix=NOFTZ %s
 
 
 // CPUFTZ-NOT: -fdenormal-fp-math