Add a "probe-stack" attribute

This attribute is used to ensure the guard page is triggered on stack
overflow. Stack frames larger than the guard page size will generate
a call to __probestack to touch each page so the guard page won't
be skipped.

Reviewed By: majnemer

Differential Revision: https://reviews.llvm.org/D34386

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@305939 91177308-0d34-0410-b5e6-96231b3b80d8

docs/LangRef.rst

@@ -1467,6 +1467,19 @@ example:
     This attribute by itself does not imply restrictions on
     inter-procedural optimizations.  All of the semantic effects the
     patching may have to be separately conveyed via the linkage type.
+``"probe-stack"``
+    This attribute indicates that the function will trigger a guard region
+    in the end of the stack. It ensures that accesses to the stack must be
+    no further apart than the size of the guard region to a previous
+    access of the stack. It takes one required string value, the name of
+    the stack probing function that will be called.
+
+    If a function that has a ``"probe-stack"`` attribute is inlined into
+    a function with another ``"probe-stack"`` attribute, the resulting
+    function has the ``"probe-stack"`` attribute of the caller. If a
+    function that has a ``"probe-stack"`` attribute is inlined into a
+    function that has no ``"probe-stack"`` attribute at all, the resulting
+    function has the ``"probe-stack"`` attribute of the callee.
 ``readnone``
     On a function, this attribute indicates that the function computes its
     result (or decides to unwind an exception) based strictly on its arguments,

include/llvm/IR/Attributes.td

@@ -211,3 +211,4 @@ def : MergeRule<"setAND<UnsafeFPMathAttr>">;
 def : MergeRule<"setOR<NoImplicitFloatAttr>">;
 def : MergeRule<"setOR<NoJumpTablesAttr>">;
 def : MergeRule<"adjustCallerSSPLevel">;
+def : MergeRule<"adjustCallerStackProbes">;

lib/IR/Attributes.cpp

@@ -1502,6 +1502,13 @@ static void adjustCallerSSPLevel(Function &Caller, const Function &Callee) {
     Caller.addFnAttr(Attribute::StackProtect);
 }
 
+/// \brief If the inlined function required stack probes, then ensure that
+/// the calling function has those too.
+static void adjustCallerStackProbes(Function &Caller, const Function &Callee) {
+  if (!Caller.hasFnAttribute("probe-stack") && Callee.hasFnAttribute("probe-stack"))
+    Caller.addFnAttr("probe-stack", Callee.getFnAttribute("probe-stack").getValueAsString());
+}
+
 #define GET_ATTR_COMPAT_FUNC
 #include "AttributesCompatFunc.inc"
 

test/Transforms/Inline/inline-probe-stack.ll

@@ -0,0 +1,20 @@
+; RUN: opt %s -inline -S | FileCheck %s
+
+define internal void @inner() "probe-stack"="__probestackinner" {
+  ret void
+}
+
+define void @outerNoAttribute() {
+  call void @inner()
+  ret void
+}
+
+define void @outerConflictingAttribute() "probe-stack"="__probestackouter" {
+  call void @inner()
+  ret void
+}
+
+; CHECK: define void @outerNoAttribute() #0
+; CHECK: define void @outerConflictingAttribute() #1
+; CHECK: attributes #0 = { "probe-stack"="__probestackinner" }
+; CHECK: attributes #1 = { "probe-stack"="__probestackouter" }