clang: Don't warn on unused momit-leaf-frame-pointer when frame pointers are off.

This fixes a regression from r365860: As that commit message
states, there are 3 valid states targeted by the combination of
-f(no-)omit-frame-pointer and -m(no-)omit-leaf-frame-pointer.

After r365860 it's impossible to get from state 10 (omit just
leaf frame pointers) to state 11 (omit all frame pointers)
in a single command line without getting a warning.

This change restores that functionality.

Fixes PR42966.

Differential Revision: https://reviews.llvm.org/D66142

llvm-svn: 368728

Author: nico

clang/lib/Driver/ToolChains/Clang.cpp

@@ -580,16 +580,27 @@ static bool useFramePointerForTargetByDefault(const ArgList &Args,
 
 static CodeGenOptions::FramePointerKind
 getFramePointerKind(const ArgList &Args, const llvm::Triple &Triple) {
+  // We have 4 states:
+  //
+  //  00) leaf retained, non-leaf retained
+  //  01) leaf retained, non-leaf omitted (this is invalid)
+  //  10) leaf omitted, non-leaf retained
+  //      (what -momit-leaf-frame-pointer was designed for)
+  //  11) leaf omitted, non-leaf omitted
+  //
+  //  "omit" options taking precedence over "no-omit" options is the only way
+  //  to make 3 valid states representable
   Arg *A = Args.getLastArg(options::OPT_fomit_frame_pointer,
                            options::OPT_fno_omit_frame_pointer);
   bool OmitFP = A && A->getOption().matches(options::OPT_fomit_frame_pointer);
   bool NoOmitFP =
       A && A->getOption().matches(options::OPT_fno_omit_frame_pointer);
+  bool KeepLeaf =
+      Args.hasFlag(options::OPT_momit_leaf_frame_pointer,
+                   options::OPT_mno_omit_leaf_frame_pointer, Triple.isPS4CPU());
   if (NoOmitFP || mustUseNonLeafFramePointerForTarget(Triple) ||
       (!OmitFP && useFramePointerForTargetByDefault(Args, Triple))) {
-    if (Args.hasFlag(options::OPT_momit_leaf_frame_pointer,
-                     options::OPT_mno_omit_leaf_frame_pointer,
-                     Triple.isPS4CPU()))
+    if (KeepLeaf)
       return CodeGenOptions::FramePointerKind::NonLeaf;
     return CodeGenOptions::FramePointerKind::All;
   }

clang/test/Driver/frame-pointer-elim.c

@@ -1,5 +1,8 @@
+// KEEP-ALL-NOT:  warning:
 // KEEP-ALL:      "-mframe-pointer=all"
+// KEEP-NON-LEAF-NOT: warning:
 // KEEP-NON-LEAF: "-mframe-pointer=non-leaf"
+// KEEP-NONE-NOT: warning:
 // KEEP-NONE:     "-mframe-pointer=none"
 
 // On Linux x86, omit frame pointer when optimization is enabled.
@@ -25,6 +28,13 @@
 // RUN: %clang -### -target i386-linux -S -O1 -momit-leaf-frame-pointer %s 2>&1 | \
 // RUN:   FileCheck --check-prefix=KEEP-NONE %s
 
+// fno-omit-frame-pointer -momit-leaf-frame-pointer can be overwritten by
+// fomit-frame-pointer later on the command without warning
+// RUN: %clang -### -target i386-linux -S -O1 -fno-omit-frame-pointer -momit-leaf-frame-pointer -fomit-frame-pointer %s 2>&1 | \
+// RUN:   FileCheck --check-prefix=KEEP-NONE %s
+
+// RUN: %clang -### -target i386-linux -S -O1 -fno-omit-frame-pointer -momit-leaf-frame-pointer %s 2>&1 | \
+// RUN:   FileCheck --check-prefix=KEEP-NON-LEAF %s
 // Explicit or default -fomit-frame-pointer wins over -mno-omit-leaf-frame-pointer.
 // RUN: %clang -### -target i386 -S %s -fomit-frame-pointer -mno-omit-leaf-frame-pointer 2>&1 | \
 // RUN:   FileCheck --check-prefix=KEEP-NONE %s