[PowerPC] Diagnose invalid combination with Altivec, VSX and soft-float

[nemanjai]

Summary

The current behaviour with these three options is quite undesirable:
-mno-altivec -mvsx allows VSX to override no Altivec, thereby turning on both
-msoft-float -maltivec causes a crash if an actual Altivec instruction is required because soft float turns of Altivec
-msoft-float -mvsx is also accepted with both Altivec and VSX turned off (potentially causing crashes as above)

This patch diagnoses these impossible combinations in the driver so the user does not end up with surprises in terms of their options being ignored or silently overridden.

Inspired by https://github.com/llvm/llvm-project/issues/55556

[Laurentiu]

Hi Nemanja,

I just realized I only had a personal account on llvm.org. Would you be
able to remove me from that review and add [e-mail]
instead?

Thanks,
Laurentiu

[ltertan]

clang/lib/Basic/Targets/PPC.cpp

455

Do we also need to return from here?

461

Do we also need to return from here?

[qiucf]

clang/lib/Basic/Targets/PPC.cpp

450

Comments in reverse order?

[amyk]

clang/lib/Basic/Targets/PPC.cpp

452

Do we also need a case to represent -msoft-float and -mvsx?

clang/lib/Basic/Targets/PPC.cpp

 // - paired-vector-memops
 // - mma
 // - power10-vector
 // then go ahead and error since the customer has expressed an incompatible
 // set of options.
 static bool ppcUserFeaturesCheck(DiagnosticsEngine &Diags,
                                  const std::vector<std::string> &FeaturesVec) {
 
+  // Cannot allow VSX with no Altivec.
+  if (llvm::is_contained(FeaturesVec, "-hard-float") &&
+      llvm::is_contained(FeaturesVec, "+altivec"))
+    Diags.Report(diag::err_opt_not_valid_with_opt) << "-msoft-float"
+                                                   << "-maltivec";
+
+  // Cannot allow soft-float with Altivec.
+  if (llvm::is_contained(FeaturesVec, "+vsx") &&
+      llvm::is_contained(FeaturesVec, "-altivec"))
+    Diags.Report(diag::err_opt_not_valid_with_opt) << "-mvsx"
+                                                   << "-mno-altivec";
+
   // vsx was not explicitly turned off.
   if (!llvm::is_contained(FeaturesVec, "-vsx"))
     return true;
 
   auto FindVSXSubfeature = [&](StringRef Feature, StringRef Option) {
     if (llvm::is_contained(FeaturesVec, Feature)) {
       Diags.Report(diag::err_opt_not_valid_with_opt) << Option << "-mno-vsx";
       return true;

clang/test/CodeGen/PowerPC/attr-target-ppc.c

 // RUN: not %clang_cc1 -triple powerpc64le-linux-gnu -emit-llvm %s -o -
 
 long __attribute__((target("power8-vector,no-vsx"))) foo (void) { return 0; }  // expected-error {{option '-mpower8-vector' cannot be specified with '-mno-vsx'}}
-
+long __attribute__((target("no-altivec,vsx"))) foo2(void) { return 0; }        // expected-error {{option '-mvsx' cannot be specified with '-mno-altivec'}}
+long __attribute__((target("no-hard-float,altivec"))) foo3(void) { return 0; } // expected-error {{option '-msoft-float' cannot be specified with '-maltivec'}}

clang/test/Driver/ppc-dependent-options.cpp

 // RUN: not %clang -target powerpc64le-unknown-unknown -fsyntax-only \
 // RUN: -mcpu=power10 -std=c++11 %s 2>&1 | FileCheck %s \
 // RUN: -check-prefix=CHECK-DEFAULT-P10
 
 // RUN: not %clang -target powerpc64le-unknown-unknown -fsyntax-only \
 // RUN: -mcpu=power10 -std=c++11 -mno-vsx -mpower10-vector %s 2>&1 | \
 // RUN: FileCheck %s -check-prefix=CHECK-NVSX-P10V
 
+// RUN: not %clang -target powerpc64le-unknown-unknown -fsyntax-only \
+// RUN: -std=c++11 -mvsx -mno-altivec %s 2>&1 | \
+// RUN: FileCheck %s -check-prefix=CHECK-NALTI-VSX
+
+// RUN: not %clang -target powerpc64le-unknown-unknown -fsyntax-only \
+// RUN: -std=c++11 -msoft-float -maltivec %s 2>&1 | \
+// RUN: FileCheck %s -check-prefix=CHECK-SOFTFLT-ALTI
+
 #ifdef __VSX__
 static_assert(false, "VSX enabled");
 #endif
 
 #ifdef __POWER8_VECTOR__
 static_assert(false, "P8V enabled");
 #endif
 

 // CHECK-NVSX-P9V: error: option '-mpower9-vector' cannot be specified with '-mno-vsx'
 // CHECK-NVSX-P10V: error: option '-mpower10-vector' cannot be specified with '-mno-vsx'
 // CHECK-NVSX-FLT128: error: option '-mfloat128' cannot be specified with '-mno-vsx'
 // CHECK-NVSX-DMV: error: option '-mdirect-move' cannot be specified with '-mno-vsx'
 // CHECK-NVSX-PAIRED-VEC-MEMOPS: error: option '-mpaired-vector-memops' cannot be specified with '-mno-vsx'
 // CHECK-NVSX-MULTI: error: option '-mfloat128' cannot be specified with '-mno-vsx'
 // CHECK-NVSX-MULTI: error: option '-mpower9-vector' cannot be specified with '-mno-vsx'
 // CHECK-NVSX-MMA: error: option '-mmma' cannot be specified with '-mno-vsx'
+// CHECK-NALTI-VSX: error: option '-mvsx' cannot be specified with '-mno-altivec'
+// CHECK-SOFTFLT-ALTI: error: option '-msoft-float' cannot be specified with '-maltivec'
 // CHECK-NVSX: Neither enabled
 // CHECK-VSX: VSX enabled