[optnone] Make the optnone attribute effective at suppressing function

attribute and function argument attribute synthesizing and propagating.

As with the other uses of this attribute, the goal remains a best-effort
(no guarantees) attempt to not optimize the function or assume things
about the function when optimizing. This is particularly useful for
compiler testing, bisecting miscompiles, triaging things, etc. I was
hitting specific issues using optnone to isolate test code from a test
driver for my fuzz testing, and this is one step of fixing that.

llvm-svn: 215538

Author: chandlerc

llvm/lib/Transforms/IPO/FunctionAttrs.cpp

@@ -161,8 +161,9 @@ bool FunctionAttrs::AddReadAttrs(const CallGraphSCC &SCC) {
   for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
     Function *F = (*I)->getFunction();
 
-    if (!F)
-      // External node - may write memory.  Just give up.
+    if (!F || F->hasFnAttribute(Attribute::OptimizeNone))
+      // External node or node we don't want to optimize - assume it may write
+      // memory and give up.
       return false;
 
     AliasAnalysis::ModRefBehavior MRB = AA->getModRefBehavior(F);
@@ -527,7 +528,8 @@ bool FunctionAttrs::AddArgumentAttrs(const CallGraphSCC &SCC) {
   // looking up whether a given CallGraphNode is in this SCC.
   for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
     Function *F = (*I)->getFunction();
-    if (F && !F->isDeclaration() && !F->mayBeOverridden())
+    if (F && !F->isDeclaration() && !F->mayBeOverridden() &&
+        !F->hasFnAttribute(Attribute::OptimizeNone))
       SCCNodes.insert(F);
   }
 
@@ -541,8 +543,9 @@ bool FunctionAttrs::AddArgumentAttrs(const CallGraphSCC &SCC) {
   for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
     Function *F = (*I)->getFunction();
 
-    if (!F)
-      // External node - only a problem for arguments that we pass to it.
+    if (!F || F->hasFnAttribute(Attribute::OptimizeNone))
+      // External node or function we're trying not to optimize - only a problem
+      // for arguments that we pass to it.
       continue;
 
     // Definitions with weak linkage may be overridden at linktime with
@@ -794,8 +797,8 @@ bool FunctionAttrs::AddNoAliasAttrs(const CallGraphSCC &SCC) {
   for (CallGraphSCC::iterator I = SCC.begin(), E = SCC.end(); I != E; ++I) {
     Function *F = (*I)->getFunction();
 
-    if (!F)
-      // External node - skip it;
+    if (!F || F->hasFnAttribute(Attribute::OptimizeNone))
+      // External node or node we don't want to optimize - skip it;
       return false;
 
     // Already noalias.
@@ -834,6 +837,9 @@ bool FunctionAttrs::AddNoAliasAttrs(const CallGraphSCC &SCC) {
 /// given function and set any applicable attributes.  Returns true
 /// if any attributes were set and false otherwise.
 bool FunctionAttrs::inferPrototypeAttributes(Function &F) {
+  if (F.hasFnAttribute(Attribute::OptimizeNone))
+    return false;
+
   FunctionType *FTy = F.getFunctionType();
   LibFunc::Func TheLibFunc;
   if (!(TLI->getLibFunc(F.getName(), TheLibFunc) && TLI->has(TheLibFunc)))

llvm/test/Transforms/FunctionAttrs/optnone.ll

@@ -0,0 +1,24 @@
+; RUN: opt < %s -functionattrs -S | FileCheck %s
+
+@x = global i32 0
+
+define void @test_opt(i8* %p) {
+; CHECK-LABEL: @test_opt
+; CHECK: (i8* nocapture readnone %p) #0 {
+  ret void
+}
+
+define void @test_optnone(i8* %p) noinline optnone {
+; CHECK-LABEL: @test_optnone
+; CHECK: (i8* %p) #1 {
+  ret void
+}
+
+declare i8 @strlen(i8*) noinline optnone
+; CHECK-LABEL: @strlen
+; CHECK: (i8*) #1
+
+; CHECK-LABEL: attributes #0
+; CHECK: = { readnone }
+; CHECK-LABEL: attributes #1
+; CHECK: = { noinline optnone }