IRGen: Add optnone attribute on function during O0

Amongst other, this will help LTO to correctly handle/honor files
compiled with O0, helping debugging failures.
It also seems in line with how we handle other options, like how
-fnoinline adds the appropriate attribute as well.

Differential Revision: https://reviews.llvm.org/D28404

llvm-svn: 304127

1 files changed, 12 insertions, 2 deletions

diff --git a/clang/lib/CodeGen/CodeGenModule.cpp b/clang/lib/CodeGen/CodeGenModule.cpp
index ffbcbfcc291..e4e5fce0227 100644
--- a/clang/lib/CodeGen/CodeGenModule.cpp
+++ b/clang/lib/CodeGen/CodeGenModule.cpp
@@ -907,7 +907,16 @@ void CodeGenModule::SetLLVMFunctionAttributesForDefinition(const Decl *D,
     return;
   }
 
-  if (D->hasAttr<OptimizeNoneAttr>()) {
+  // Track whether we need to add the optnone LLVM attribute,
+  // starting with the default for this optimization level.
+  bool ShouldAddOptNone =
+      !CodeGenOpts.DisableO0ImplyOptNone && CodeGenOpts.OptimizationLevel == 0;
+  // We can't add optnone in the following cases, it won't pass the verifier.
+  ShouldAddOptNone &= !D->hasAttr<MinSizeAttr>();
+  ShouldAddOptNone &= !F->hasFnAttribute(llvm::Attribute::AlwaysInline);
+  ShouldAddOptNone &= !D->hasAttr<AlwaysInlineAttr>();
+
+  if (ShouldAddOptNone || D->hasAttr<OptimizeNoneAttr>()) {
     B.addAttribute(llvm::Attribute::OptimizeNone);
 
     // OptimizeNone implies noinline; we should not be inlining such functions.
@@ -961,7 +970,8 @@ void CodeGenModule::SetLLVMFunctionAttributesForDefinition(const Decl *D,
   // function.
   if (!D->hasAttr<OptimizeNoneAttr>()) {
     if (D->hasAttr<ColdAttr>()) {
-      B.addAttribute(llvm::Attribute::OptimizeForSize);
+      if (!ShouldAddOptNone)
+        B.addAttribute(llvm::Attribute::OptimizeForSize);
       B.addAttribute(llvm::Attribute::Cold);
     }