[StackProtector] Ignore certain intrinsics when calculating sspstrong heuristic.

[mattd]

Summary

The 'strong' StackProtector heuristic takes into consideration call instructions.
Certain intrinsics, such as lifetime.start, can cause the
StackProtector to protect functions that do not need to be protected.

Specifically, a volatile variable, (not optimized away), but belonging to a stack
allocation will encourage a llvm.lifetime.start to be inserted during
compilation. Because that intrinsic is a 'call' the strong StackProtector
will see that the alloca'd variable is being passed to a call instruction, and
insert a stack protector. In this case the intrinsic isn't really lowered to a
call. This can cause unnecessary stack checking, at the cost of additional
(wasted) CPU cycles.

In the future we should rely on TargetTransformInfo::isLoweredToCall, but as of
now that routine considers all intrinsics as not being lowerable. That needs
to be corrected, and such a change is on my list of things to get moving on.

As a side note, the updated stack-protector-dbginfo.ll test always seems to
pass. I never see the dbg.declare/dbg.value reaching the
StackProtector::HasAddressTaken, but I don't see any code excluding dbg
intrinsic calls either, so I think it's the safest thing to do.

[timshen]

In the future we should rely on TargetTransformInfo::isLoweredToCall, but as of

now that routine considers all intrinsics as not being lowerable.

Can we just add lifetime intrinsics support into TTI::isLoweredToCall() ? Will it break other things? If it's doable, then the stackprotector just needs to call isLoweredToCall().

[mattd]

In D45331#1059258, @timshen wrote:

In the future we should rely on TargetTransformInfo::isLoweredToCall, but as of
now that routine considers all intrinsics as not being lowerable.

Can we just add lifetime intrinsics support into TTI::isLoweredToCall() ? Will it break other things? If it's doable, then the stackprotector just needs to call isLoweredToCall().

I'm hesitant to modify isLoweredToCall right now, as I think it will need more work to decide whether a particular intrinsic is lowerable. For now, I figure we just put a
check to avoid counting the lifetime/debug intrinsics in this heuristic. It seems checks similar to the ones in this patch are pretty common throughout the codebase, at least for ignoring debug intrinsics.

[timshen]

Sounds good, as it is not hard to track down and inspect all lifetime intrinsic heuristics in the future for using the improved isLoweredToCall().

lib/CodeGen/StackProtector.cpp

 #include "llvm/IR/DebugInfo.h"
 #include "llvm/IR/DebugLoc.h"
 #include "llvm/IR/DerivedTypes.h"
 #include "llvm/IR/Dominators.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/IRBuilder.h"
 #include "llvm/IR/Instruction.h"
 #include "llvm/IR/Instructions.h"
+#include "llvm/IR/IntrinsicInst.h"
 #include "llvm/IR/Intrinsics.h"
 #include "llvm/IR/MDBuilder.h"
 #include "llvm/IR/Module.h"
 #include "llvm/IR/Type.h"
 #include "llvm/IR/User.h"
 #include "llvm/Pass.h"
 #include "llvm/Support/Casting.h"
 #include "llvm/Support/CommandLine.h"
if (ContainsProtectableArray(*I, IsLarge, Strong, true)) {
       if (IsLarge)
         return true;
       NeedsProtector = true;
     }
 
   return NeedsProtector;
 }
 
+static bool isLifetimeInst(const Instruction *I) {
+  if (const auto Intrinsic = dyn_cast<IntrinsicInst>(I)) {
+    const auto Id = Intrinsic->getIntrinsicID();
+    return Id == Intrinsic::lifetime_start || Id == Intrinsic::lifetime_end;
+  }
+  return false;
+}
+
 bool StackProtector::HasAddressTaken(const Instruction *AI) {
   for (const User *U : AI->users()) {
     if (const StoreInst *SI = dyn_cast<StoreInst>(U)) {
       if (AI == SI->getValueOperand())
         return true;
     } else if (const PtrToIntInst *SI = dyn_cast<PtrToIntInst>(U)) {
       if (AI == SI->getOperand(0))
         return true;
-    } else if (isa<CallInst>(U)) {
+    } else if (const CallInst *CI = dyn_cast<CallInst>(U)) {
+      // Ignore intrinsics that are not calls. TODO: Use isLoweredToCall().
+      if (!isa<DbgInfoIntrinsic>(CI) && !isLifetimeInst(CI))
         return true;
     } else if (isa<InvokeInst>(U)) {
       return true;
     } else if (const SelectInst *SI = dyn_cast<SelectInst>(U)) {
       if (HasAddressTaken(SI))
         return true;
     } else if (const PHINode *PN = dyn_cast<PHINode>(U)) {
       // Keep track of what PHI nodes we have already visited to ensure
       // they are only visited once.

test/CodeGen/X86/stack-protector-dbginfo.ll

 ; RUN: llc -mtriple=x86_64-apple-darwin < %s -o -
+; RUN: llc -mtriple=x86_64-pc-linux-gnu < %s -o - | FileCheck --check-prefix=IGNORE_INTRIN %s
 
 ; PR16954
 ;
 ; Make sure that when we splice off the end of a machine basic block, we include
 ; DBG_VALUE MI in the terminator sequence.
 
 @a = external global { i64, [56 x i8] }, align 32
 
 ; Function Attrs: nounwind sspreq
 define i32 @_Z18read_response_sizev() #0 !dbg !9 {
 entry:
   tail call void @llvm.dbg.value(metadata !22, i64 0, metadata !23, metadata !DIExpression()), !dbg !39
   %0 = load i64, i64* getelementptr inbounds ({ i64, [56 x i8] }, { i64, [56 x i8] }* @a, i32 0, i32 0), align 8, !dbg !40
   tail call void @llvm.dbg.value(metadata i32 undef, i64 0, metadata !64, metadata !DIExpression()), !dbg !71
   %1 = trunc i64 %0 to i32
   ret i32 %1
 }
 
+define i32 @IgnoreIntrinsicTest() #1 {
+; IGNORE_INTRIN: IgnoreIntrinsicTest:
+  %1 = alloca i32, align 4
+  %2 = bitcast i32* %1 to i8*
+  call void @llvm.dbg.declare(metadata i32* %1, metadata !73, metadata !DIExpression()), !dbg !74
+  store volatile i32 1, i32* %1, align 4
+  %3 = load volatile i32, i32* %1, align 4
+  %4 = mul nsw i32 %3, 42
+  ret i32 %4
+; IGNORE_INTRIN-NOT: callq __stack_chk_fail
+; IGNORE_INTRIN:     .cfi_endproc
+}
+
 ; Function Attrs: nounwind readnone
 declare void @llvm.dbg.value(metadata, i64, metadata, metadata)
+declare void @llvm.dbg.declare(metadata, metadata, metadata)
 
 attributes #0 = { sspreq }
 
 !llvm.dbg.cu = !{!0}
 !llvm.module.flags = !{!21, !72}
 
 !0 = distinct !DICompileUnit(language: DW_LANG_C_plus_plus, producer: "clang version 3.4 ", isOptimized: true, emissionKind: FullDebug, file: !1, enums: !2, retainedTypes: !5, globals: !20, imports: !5)
 !1 = !DIFile(filename: "<unknown>", directory: "/Users/matt/ryan_bug")

 !65 = distinct !DISubprogram(name: "operator()", linkageName: "_ZN3__11AclERKiS2_", line: 1, isLocal: false, isDefinition: true, virtualIndex: 6, flags: DIFlagPrototyped, isOptimized: true, unit: !0, scopeLine: 2, file: !1, scope: !25, type: !47, declaration: !46, variables: !66)
 !66 = !{!67, !69, !70}
 !67 = !DILocalVariable(name: "this", arg: 1, flags: DIFlagArtificial | DIFlagObjectPointer, scope: !65, type: !68)
 !68 = !DIDerivedType(tag: DW_TAG_pointer_type, size: 64, align: 64, baseType: !44)
 !69 = !DILocalVariable(name: "p1", line: 1, arg: 2, scope: !65, file: !10, type: !50)
 !70 = !DILocalVariable(name: "", line: 2, arg: 3, scope: !65, file: !10, type: !50)
 !71 = !DILocation(line: 1, scope: !65, inlinedAt: !40)
 !72 = !{i32 1, !"Debug Info Version", i32 3}
+!73 = !DILocalVariable(name: "x", scope: !74, file: !1, line: 2, type: !13)
+!74 = distinct !DISubprogram(name: "IgnoreIntrinsicTest", linkageName: "IgnoreIntrinsicTest", scope: !1, file: !1, line: 1, type: !13, isLocal: false, isDefinition: true, scopeLine: 1, flags: DIFlagPrototyped, isOptimized: true, unit: !0, variables: !5)
+!75 = !DILocation(line: 2, column: 16, scope: !7)

test/CodeGen/X86/stack-protector.ll

 ; RUN: llc -mtriple=i386-pc-linux-gnu < %s -o - | FileCheck --check-prefix=LINUX-I386 %s
 ; RUN: llc -mtriple=x86_64-pc-linux-gnu < %s -o - | FileCheck --check-prefix=LINUX-X64 %s
 ; RUN: llc -code-model=kernel -mtriple=x86_64-pc-linux-gnu < %s -o - | FileCheck --check-prefix=LINUX-KERNEL-X64 %s
 ; RUN: llc -mtriple=x86_64-apple-darwin < %s -o - | FileCheck --check-prefix=DARWIN-X64 %s
 ; RUN: llc -mtriple=amd64-pc-openbsd < %s -o - | FileCheck --check-prefix=OPENBSD-AMD64 %s
 ; RUN: llc -mtriple=i386-pc-windows-msvc < %s -o - | FileCheck -check-prefix=MSVC-I386 %s
 ; RUN: llc -mtriple=x86_64-w64-mingw32 < %s -o - | FileCheck --check-prefix=MINGW-X64 %s
+; RUN: llc -mtriple=x86_64-pc-linux-gnu < %s -o - | FileCheck --check-prefix=IGNORE_INTRIN %s
 
 %struct.foo = type { [16 x i8] }
 %struct.foo.0 = type { [4 x i8] }
 %struct.pair = type { i32, i32 }
 %struct.nest = type { %struct.pair, %struct.pair }
 %struct.vec = type { <4 x i32> }
 %class.A = type { [2 x i8] }
 %struct.deep = type { %union.anon }

 ; OPENBSD-AMD64:       .loc 1 4 2 prologue_end
 ; OPENBSD-AMD64:       .loc 1 0 0
 ; OPENBSD-AMD64-NEXT:  movl
 ; OPENBSD-AMD64-NEXT:  callq __stack_smash_handler
   %0 = alloca [5 x i8], align 1
   ret void, !dbg !9
 }
 
+define i32 @IgnoreIntrinsicTest() #1 {
+; IGNORE_INTRIN: IgnoreIntrinsicTest:
+  %1 = alloca i32, align 4
+  %2 = bitcast i32* %1 to i8*
+  call void @llvm.lifetime.start.p0i8(i64 4, i8* nonnull %2)
+  store volatile i32 1, i32* %1, align 4
+  %3 = load volatile i32, i32* %1, align 4
+  %4 = mul nsw i32 %3, 42
+  call void @llvm.lifetime.end.p0i8(i64 4, i8* nonnull %2)
+  ret i32 %4
+; IGNORE_INTRIN-NOT: callq __stack_chk_fail
+; IGNORE_INTRIN:     .cfi_endproc
+}
+
 declare double @testi_aux()
 declare i8* @strcpy(i8*, i8*)
 declare i32 @printf(i8*, ...)
 declare void @funcall(i32*)
 declare void @funcall2(i32**)
 declare void @funfloat(float*)
 declare void @funfloat2(float**)
 declare void @_Z3exceptPi(i32*)
 declare i32 @__gxx_personality_v0(...)
 declare i32* @getp()
 declare i32 @dummy(...)
 declare void @llvm.memcpy.p0i8.p0i8.i64(i8* nocapture, i8* nocapture readonly, i64, i1)
+declare void @llvm.lifetime.start.p0i8(i64, i8* nocapture)
+declare void @llvm.lifetime.end.p0i8(i64, i8* nocapture)
 
 attributes #0 = { ssp }
 attributes #1 = { sspstrong }
 attributes #2 = { sspreq }
 attributes #3 = { ssp "stack-protector-buffer-size"="33" }
 attributes #4 = { ssp "stack-protector-buffer-size"="5" }
 attributes #5 = { ssp "stack-protector-buffer-size"="6" }