[PowerPC] Diagnose invalid combination with Altivec, VSX and soft-float (#79109)

Moved from https://reviews.llvm.org/D126302

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.

Fixes #55556

---------

Co-authored-by: Nemanja Ivanovic <[email protected]>

Author: Chen Zheng

clang/lib/Basic/Targets/PPC.cpp

@@ -442,19 +442,44 @@ void PPCTargetInfo::getTargetDefines(const LangOptions &Opts,
   //   _CALL_DARWIN
 }
 
-// Handle explicit options being passed to the compiler here: if we've
-// explicitly turned off vsx and turned on any of:
-// - power8-vector
-// - direct-move
-// - float128
-// - power9-vector
-// - paired-vector-memops
-// - mma
-// - power10-vector
+// Handle explicit options being passed to the compiler here:
+// - if we've explicitly turned off vsx and turned on any of:
+//   - power8-vector
+//   - direct-move
+//   - float128
+//   - power9-vector
+//   - paired-vector-memops
+//   - mma
+//   - power10-vector
+// - if we've explicitly turned on vsx and turned off altivec.
+// - if we've explicitly turned off hard-float and turned on altivec.
 // 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 soft-float with 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";
+    return false;
+  }
+
+  // Cannot allow soft-float with VSX.
+  if (llvm::is_contained(FeaturesVec, "-hard-float") &&
+      llvm::is_contained(FeaturesVec, "+vsx")) {
+    Diags.Report(diag::err_opt_not_valid_with_opt) << "-msoft-float"
+                                                   << "-mvsx";
+    return false;
+  }
+
+  // Cannot allow VSX with no Altivec.
+  if (llvm::is_contained(FeaturesVec, "+vsx") &&
+      llvm::is_contained(FeaturesVec, "-altivec")) {
+    Diags.Report(diag::err_opt_not_valid_with_opt) << "-mvsx"
+                                                   << "-mno-altivec";
+    return false;
+  }
 
   // vsx was not explicitly turned off.
   if (!llvm::is_contained(FeaturesVec, "-vsx"))

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

@@ -1,4 +1,7 @@
 // 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'}}
+long __attribute__((target("no-hard-float,vsx"))) foo4(void) { return 0; } // expected-error {{option '-msoft-float' cannot be specified with '-mvsx'}}
 

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

@@ -78,6 +78,18 @@
 // 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
+
+// RUN: not %clang -target powerpc64le-unknown-unknown -fsyntax-only \
+// RUN: -std=c++11 -msoft-float -mvsx %s 2>&1 | \
+// RUN: FileCheck %s -check-prefix=CHECK-SOFTFLT-VSX
+
 #ifdef __VSX__
 static_assert(false, "VSX enabled");
 #endif
@@ -114,3 +126,6 @@ static_assert(false, "Neither enabled");
 // CHECK-NVSX-MMA: error: option '-mmma' cannot be specified with '-mno-vsx'
 // CHECK-NVSX: Neither enabled
 // CHECK-VSX: VSX enabled
+// 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-SOFTFLT-VSX: error: option '-msoft-float' cannot be specified with '-mvsx'