r345826 - CPU-Dispatch-- Fix conflict between 'generic' and 'pentium'

[Erich Keane via cfe-commits]

Author: erichkeane
Date: Thu Nov  1 05:50:37 2018
New Revision: 345826

URL: http://llvm.org/viewvc/llvm-project?rev=345826&view=rev
Log:
CPU-Dispatch-- Fix conflict between 'generic' and 'pentium'

When a dispatch function was being emitted that had both a generic and a
pentium configuration listed, we would assert.  This is because neither
configuration has any 'features' associated with it so they were both
considered the 'default' version.  'pentium' lacks any features because
we implement it in terms of __builtin_cpu_supports (instead of Intel
proprietary checks), which is unable to decern between the two.

The fix for this is to omit the 'generic' version from the dispatcher if
both are present. This permits existing code to compile, and still will
choose the 'best' version available (since 'pentium' is technically
better than 'generic').

Change-Id: I4b69f3e0344e74cbdbb04497845d5895dd05fda0

Modified:
    cfe/trunk/lib/CodeGen/CodeGenModule.cpp
    cfe/trunk/test/CodeGen/attr-cpuspecific.c

Modified: cfe/trunk/lib/CodeGen/CodeGenModule.cpp
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CodeGenModule.cpp?rev=345826&r1=345825&r2=345826&view=diff
==============================================================================
--- cfe/trunk/lib/CodeGen/CodeGenModule.cpp (original)
+++ cfe/trunk/lib/CodeGen/CodeGenModule.cpp Thu Nov  1 05:50:37 2018
@@ -2583,6 +2583,22 @@ void CodeGenModule::emitCPUDispatchDefin
         return CodeGenFunction::GetX86CpuSupportsMask(LHS.Conditions.Features) >
                CodeGenFunction::GetX86CpuSupportsMask(RHS.Conditions.Features);
       });
+
+  // If the list contains multiple 'default' versions, such as when it contains
+  // 'pentium' and 'generic', don't emit the call to the generic one (since we
+  // always run on at least a 'pentium'). We do this by deleting the 'least
+  // advanced' (read, lowest mangling letter).
+  while (Options.size() > 1 &&
+         CodeGenFunction::GetX86CpuSupportsMask(
+             (Options.end() - 2)->Conditions.Features) == 0) {
+    StringRef LHSName = (Options.end() - 2)->Function->getName();
+    StringRef RHSName = (Options.end() - 1)->Function->getName();
+    if (LHSName.compare(RHSName) < 0)
+      Options.erase(Options.end() - 2);
+    else
+      Options.erase(Options.end() - 1);
+  }
+
   CodeGenFunction CGF(*this);
   CGF.EmitMultiVersionResolver(ResolverFunc, Options);
 }

Modified: cfe/trunk/test/CodeGen/attr-cpuspecific.c
URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGen/attr-cpuspecific.c?rev=345826&r1=345825&r2=345826&view=diff
==============================================================================
--- cfe/trunk/test/CodeGen/attr-cpuspecific.c (original)
+++ cfe/trunk/test/CodeGen/attr-cpuspecific.c Thu Nov  1 05:50:37 2018
@@ -205,6 +205,24 @@ int HasParamsAndReturn(int i, double d);
 // WINDOWS-NEXT: ret i32 %[[RET]]
 // WINDOWS-NOT: call void @llvm.trap
 
+ATTR(cpu_dispatch(atom, generic, pentium))
+int GenericAndPentium(int i, double d);
+// LINUX: define i32 (i32, double)* @GenericAndPentium.resolver()
+// LINUX: call void @__cpu_indicator_init
+// LINUX: ret i32 (i32, double)* @GenericAndPentium.O
+// LINUX: ret i32 (i32, double)* @GenericAndPentium.B
+// LINUX-NOT: ret i32 (i32, double)* @GenericAndPentium.A
+// LINUX-NOT: call void @llvm.trap
+
+// WINDOWS: define dso_local i32 @GenericAndPentium(i32, double)
+// WINDOWS: call void @__cpu_indicator_init
+// WINDOWS: %[[RET:.+]] = musttail call i32 @GenericAndPentium.O(i32 %0, double %1)
+// WINDOWS-NEXT: ret i32 %[[RET]]
+// WINDOWS: %[[RET:.+]] = musttail call i32 @GenericAndPentium.B(i32 %0, double %1)
+// WINDOWS-NEXT: ret i32 %[[RET]]
+// WINDOWS-NOT: call i32 @GenericAndPentium.A
+// WINDOWS-NOT: call void @llvm.trap
+
 // CHECK: attributes #[[S]] = {{.*}}"target-features"="+avx,+cmov,+f16c,+mmx,+popcnt,+sse,+sse2,+sse3,+sse4.1,+sse4.2,+ssse3,+x87,+xsave"
 // CHECK: attributes #[[K]] = {{.*}}"target-features"="+adx,+avx,+avx2,+avx512cd,+avx512er,+avx512f,+avx512pf,+bmi,+cmov,+f16c,+fma,+lzcnt,+mmx,+movbe,+popcnt,+sse,+sse2,+sse3,+sse4.1,+sse4.2,+ssse3,+x87,+xsave"
 // CHECK: attributes #[[O]] = {{.*}}"target-features"="+cmov,+mmx,+movbe,+sse,+sse2,+sse3,+ssse3,+x87"