[Driver] Pass -plugin-opt=O2 for -Os -Oz and -plugin-opt=O1 for -Og

[MaskRay]

Summary

Fixes PR42445 (-Os -Oz translate to -plugin-opt=Os (Oz) which cannot be
recognized by LLVMgold.so or LLD).

The optimization level mapping matches
CompilerInvocation.cpp:getOptimizationLevel() and SpeedLevel of
PassBuilder::OptimizationLevel::O*.

-plugin-opt=O* affects the way we construct regular LTO/ThinLTO pass
manager pipeline.

[mehdi_amini]

LGTM, probably want @pcc to approve as well.

[pcc]

LGTM

clang/test/Driver/lto.c

52

I think this one should be --check-prefix=O2.

[MaskRay]

Thanks for the review. Will remove D79916 as a parent and commit this one first.

clang/test/Driver/lto.c

52

I added D79916 as a parent:)

Looks like I should just land this patch first and probably update the test in D79916.

[MaskRay]

-O => -O2 (temporarily, pending on the resolution of D79916)

Add a test for -Ofast

[xbolva00]

Great! Maybe worth to add a release note that -Os works with LTO?

clang/lib/Driver/ToolChains/CommonArgs.cpp

#endif
   // the plugin.
 
   // Handle flags for selecting CPU variants.
   std::string CPU = getCPUName(Args, ToolChain.getTriple());
   if (!CPU.empty())
     CmdArgs.push_back(Args.MakeArgString(Twine("-plugin-opt=mcpu=") + CPU));
 
   if (Arg *A = Args.getLastArg(options::OPT_O_Group)) {
+    // The optimization level matches
+    // CompilerInvocation.cpp:getOptimizationLevel().
     StringRef OOpt;
     if (A->getOption().matches(options::OPT_O4) ||
         A->getOption().matches(options::OPT_Ofast))
       OOpt = "3";
-    else if (A->getOption().matches(options::OPT_O))
+    else if (A->getOption().matches(options::OPT_O)) {
       OOpt = A->getValue();
-    else if (A->getOption().matches(options::OPT_O0))
+      if (OOpt == "g")
+        OOpt = "1";
+      else if (OOpt == "s" || OOpt == "z")
+        OOpt = "2";
+    } else if (A->getOption().matches(options::OPT_O0))
       OOpt = "0";
     if (!OOpt.empty())
       CmdArgs.push_back(Args.MakeArgString(Twine("-plugin-opt=O") + OOpt));
   }
 
   if (Args.hasArg(options::OPT_gsplit_dwarf)) {
     CmdArgs.push_back(
         Args.MakeArgString(Twine("-plugin-opt=dwo_dir=") +

clang/test/Driver/lto.c

 
 /// lld does not need LLVMgold.
 // RUN: %clang -target x86_64-unknown-linux-gnu --sysroot %S/Inputs/basic_cross_linux_tree %s \
 // RUN:   -fuse-ld=lld -flto -### 2>&1 | FileCheck --check-prefix=NO-LLVMGOLD %s
 // RUN: %clang -target x86_64-unknown-linux-gnu --sysroot %S/Inputs/basic_cross_linux_tree %s \
 // RUN:   -fuse-ld=gold -flto -fno-lto -### 2>&1 | FileCheck --check-prefix=NO-LLVMGOLD %s
 // NO-LLVMGOLD-NOT: "-plugin" "{{.*}}{{[/\\]}}LLVMgold.{{dll|dylib|so}}"
 
+// RUN: %clang -target x86_64-unknown-linux-gnu --sysroot %S/Inputs/basic_cross_linux_tree %s \
+// RUN:   -fuse-ld=lld -flto -O -### 2>&1 | FileCheck --check-prefix=O2 %s
+// RUN: %clang -target x86_64-unknown-linux-gnu --sysroot %S/Inputs/basic_cross_linux_tree %s \
+// RUN:   -fuse-ld=lld -flto -O1 -### 2>&1 | FileCheck --check-prefix=O1 %s
+// RUN: %clang -target x86_64-unknown-linux-gnu --sysroot %S/Inputs/basic_cross_linux_tree %s \
+// RUN:   -fuse-ld=lld -flto -Og -### 2>&1 | FileCheck --check-prefix=O1 %s
+// RUN: %clang -target x86_64-unknown-linux-gnu --sysroot %S/Inputs/basic_cross_linux_tree %s \
+// RUN:   -fuse-ld=lld -flto -O2 -### 2>&1 | FileCheck --check-prefix=O2 %s
+// RUN: %clang -target x86_64-unknown-linux-gnu --sysroot %S/Inputs/basic_cross_linux_tree %s \
+// RUN:   -fuse-ld=lld -flto -Os -### 2>&1 | FileCheck --check-prefix=O2 %s
+// RUN: %clang -target x86_64-unknown-linux-gnu --sysroot %S/Inputs/basic_cross_linux_tree %s \
+// RUN:   -fuse-ld=lld -flto -Oz -### 2>&1 | FileCheck --check-prefix=O2 %s
+// RUN: %clang -target x86_64-unknown-linux-gnu --sysroot %S/Inputs/basic_cross_linux_tree %s \
+// RUN:   -fuse-ld=lld -flto -O3 -### 2>&1 | FileCheck --check-prefix=O3 %s
+// RUN: %clang -target x86_64-unknown-linux-gnu --sysroot %S/Inputs/basic_cross_linux_tree %s \
+// RUN:   -fuse-ld=lld -flto -Ofast -### 2>&1 | FileCheck --check-prefix=O3 %s
+
+// O1: -plugin-opt=O1
+// O2: -plugin-opt=O2
+// O3: -plugin-opt=O3
+
 // -flto passes along an explicit debugger tuning argument.
 // RUN: %clang -target x86_64-unknown-linux -### %s -flto -glldb 2> %t
 // RUN: FileCheck -check-prefix=CHECK-TUNING-LLDB < %t %s
 // RUN: %clang -target x86_64-unknown-linux -### %s -flto -g 2> %t
 // RUN: FileCheck -check-prefix=CHECK-NO-TUNING < %t %s
 //
 // CHECK-TUNING-LLDB:   "-plugin-opt=-debugger-tune=lldb"
 // CHECK-NO-TUNING-NOT: "-plugin-opt=-debugger-tune