mstorsjo created this revision.
mstorsjo added reviewers: craig.topper, erichkeane, rnk.
If using a custom stack alignment, one is expected to make sure that all
callers provide such alignment, or realign the stack in all entry points (and
callbacks).
Despite this, the compiler can assume that the main function will need
realignment in these cases, since the startup routines calling the main
function most probably won't provide the custom alignment.
This matches what GCC does in similar cases; if compiling with
-mincoming-stack-boundary=X -mpreferred-stack-boundary=X, GCC normally assumes
such alignment on entry to a function, but specifically for the main function
still does realignment.
Repository:
rC Clang
https://reviews.llvm.org/D51026
Files:
lib/CodeGen/CodeGenFunction.cpp
test/CodeGen/stackrealign-main.c
Index: test/CodeGen/stackrealign-main.c
===================================================================
--- /dev/null
+++ test/CodeGen/stackrealign-main.c
@@ -0,0 +1,19 @@
+// RUN: %clang_cc1 -triple i386-unknown-unknown -emit-llvm -o -
-mstack-alignment=64 %s | FileCheck %s
+
+// CHECK-LABEL: define void @other()
+// CHECK: [[OTHER:#[0-9]+]]
+// CHECK: {
+void other(void) {}
+
+// CHECK-LABEL: define i32 @main(
+// CHECK: [[MAIN:#[0-9]+]]
+// CHECK: {
+int main(int argc, char **argv) {
+ other();
+ return 0;
+}
+
+// CHECK: attributes [[OTHER]] = { noinline nounwind optnone
+// CHECK-NOT: "stackrealign"
+// CHECK: }
+// CHECK: attributes [[MAIN]] = { noinline nounwind optnone
{{.*}}"stackrealign"{{.*}} }
Index: lib/CodeGen/CodeGenFunction.cpp
===================================================================
--- lib/CodeGen/CodeGenFunction.cpp
+++ lib/CodeGen/CodeGenFunction.cpp
@@ -981,6 +981,13 @@
if (FD->isMain())
Fn->addFnAttr(llvm::Attribute::NoRecurse);
+ // If a custom alignment is used, force realigning to this alignment on
+ // any main function which certainly will need it.
+ if (const FunctionDecl *FD = dyn_cast_or_null<FunctionDecl>(D))
+ if ((FD->isMain() || FD->isMSVCRTEntryPoint()) &&
+ CGM.getCodeGenOpts().StackAlignment)
+ Fn->addFnAttr("stackrealign");
+
llvm::BasicBlock *EntryBB = createBasicBlock("entry", CurFn);
// Create a marker to make it easy to insert allocas into the entryblock
Index: test/CodeGen/stackrealign-main.c
===================================================================
--- /dev/null
+++ test/CodeGen/stackrealign-main.c
@@ -0,0 +1,19 @@
+// RUN: %clang_cc1 -triple i386-unknown-unknown -emit-llvm -o - -mstack-alignment=64 %s | FileCheck %s
+
+// CHECK-LABEL: define void @other()
+// CHECK: [[OTHER:#[0-9]+]]
+// CHECK: {
+void other(void) {}
+
+// CHECK-LABEL: define i32 @main(
+// CHECK: [[MAIN:#[0-9]+]]
+// CHECK: {
+int main(int argc, char **argv) {
+ other();
+ return 0;
+}
+
+// CHECK: attributes [[OTHER]] = { noinline nounwind optnone
+// CHECK-NOT: "stackrealign"
+// CHECK: }
+// CHECK: attributes [[MAIN]] = { noinline nounwind optnone {{.*}}"stackrealign"{{.*}} }
Index: lib/CodeGen/CodeGenFunction.cpp
===================================================================
--- lib/CodeGen/CodeGenFunction.cpp
+++ lib/CodeGen/CodeGenFunction.cpp
@@ -981,6 +981,13 @@
if (FD->isMain())
Fn->addFnAttr(llvm::Attribute::NoRecurse);
+ // If a custom alignment is used, force realigning to this alignment on
+ // any main function which certainly will need it.
+ if (const FunctionDecl *FD = dyn_cast_or_null<FunctionDecl>(D))
+ if ((FD->isMain() || FD->isMSVCRTEntryPoint()) &&
+ CGM.getCodeGenOpts().StackAlignment)
+ Fn->addFnAttr("stackrealign");
+
llvm::BasicBlock *EntryBB = createBasicBlock("entry", CurFn);
// Create a marker to make it easy to insert allocas into the entryblock
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