[PATCH] Fix llc to not reuse spill slots in functions that invoke setjmp()

[Mark Seaborn]

Hi void,

Fix llc to not reuse spill slots in functions that invoke setjmp()

We need to ensure that StackSlotColoring.cpp does not reuse stack
spill slots in functions that call "returns_twice" functions such as
setjmp(), otherwise this can lead to miscompiled code, because a stack
slot would be clobbered when it's still live.

This was already handled correctly for functions that call setjmp()
(though this wasn't covered by a test), but not for functions that
invoke setjmp().

We fix this by changing callsFunctionThatReturnsTwice() to check for
invoke instructions.

This fixes PR18244.


http://llvm-reviews.chandlerc.com/D2543

Files:
  lib/IR/Function.cpp
  test/CodeGen/X86/setjmp-spills.ll

Index: lib/IR/Function.cpp
===================================================================
--- lib/IR/Function.cpp
+++ lib/IR/Function.cpp
@@ -736,10 +736,8 @@
 bool Function::callsFunctionThatReturnsTwice() const {
   for (const_inst_iterator
          I = inst_begin(this), E = inst_end(this); I != E; ++I) {
-    const CallInst* callInst = dyn_cast<CallInst>(&*I);
-    if (!callInst)
-      continue;
-    if (callInst->canReturnTwice())
+    ImmutableCallSite CS(&*I);
+    if (CS && CS.hasFnAttr(Attribute::ReturnsTwice))
       return true;
   }
 
Index: test/CodeGen/X86/setjmp-spills.ll
===================================================================
--- /dev/null
+++ test/CodeGen/X86/setjmp-spills.ll
@@ -0,0 +1,141 @@
+; RUN: llc < %s -mtriple=i386-linux | FileCheck %s -check-prefix=X86-32
+; RUN: llc < %s -mtriple=x86_64-linux | FileCheck %s -check-prefix=X86-64
+
+declare i32 @get_val()
+declare void @use_val(i32)
+declare i1 @setjmp()
+declare void @longjmp()
+declare void @personality()
+
+
+; Test that llc avoids reusing spill slots in functions that call
+; setjmp(), whether they use "call" or "invoke" for calling setjmp()
+; (PR18244).
+
+define void @setjmp_caller() {
+; X86-32-LABEL: setjmp_caller:
+; X86-64-LABEL: setjmp_caller:
+; This code keeps enough variables live across the setjmp() call that
+; they don't all fit in registers and the compiler will allocate a
+; spill slot.
+  %a1 = call i32 @get_val()
+  %a2 = call i32 @get_val()
+  %a3 = call i32 @get_val()
+  %a4 = call i32 @get_val()
+  %a5 = call i32 @get_val()
+  %a6 = call i32 @get_val()
+  %a7 = call i32 @get_val()
+  %a8 = call i32 @get_val()
+; X86-32: movl %eax, [[SPILL_SLOT:[0-9]+]](%esp)
+; X86-32: calll get_val
+; X86-64: movl %eax, [[SPILL_SLOT:[0-9]+]](%rsp)
+; X86-64: callq get_val
+
+  %setjmp_result = call i1 @setjmp() returns_twice
+  br i1 %setjmp_result, label %second, label %first
+; X86-32: calll setjmp
+; X86-64: callq setjmp
+
+; Again, keep enough variables live that they need spill slots.  Since
+; this function calls a returns_twice function (setjmp()), the
+; compiler should not reuse the spill slots.  longjmp() can return to
+; where the first spill slots were still live.
+first:
+  %b1 = call i32 @get_val()
+  %b2 = call i32 @get_val()
+  %b3 = call i32 @get_val()
+  %b4 = call i32 @get_val()
+  %b5 = call i32 @get_val()
+  %b6 = call i32 @get_val()
+  %b7 = call i32 @get_val()
+  %b8 = call i32 @get_val()
+  call void @use_val(i32 %b1)
+  call void @use_val(i32 %b2)
+  call void @use_val(i32 %b3)
+  call void @use_val(i32 %b4)
+  call void @use_val(i32 %b5)
+  call void @use_val(i32 %b6)
+  call void @use_val(i32 %b7)
+  call void @use_val(i32 %b8)
+  call void @longjmp()
+  unreachable
+; X86-32-NOT: movl {{.*}}, [[SPILL_SLOT]](%esp)
+; X86-64-NOT: movl {{.*}}, [[SPILL_SLOT]](%rsp)
+
+second:
+  call void @use_val(i32 %a1)
+  call void @use_val(i32 %a2)
+  call void @use_val(i32 %a3)
+  call void @use_val(i32 %a4)
+  call void @use_val(i32 %a5)
+  call void @use_val(i32 %a6)
+  call void @use_val(i32 %a7)
+  call void @use_val(i32 %a8)
+  ret void
+}
+
+
+; This is the same as above, but using "invoke" rather than "call" to
+; call setjmp().
+
+define void @setjmp_invoker() {
+; X86-32-LABEL: setjmp_invoker:
+; X86-64-LABEL: setjmp_invoker:
+  %a1 = call i32 @get_val()
+  %a2 = call i32 @get_val()
+  %a3 = call i32 @get_val()
+  %a4 = call i32 @get_val()
+  %a5 = call i32 @get_val()
+  %a6 = call i32 @get_val()
+  %a7 = call i32 @get_val()
+  %a8 = call i32 @get_val()
+; X86-32: movl %eax, [[SPILL_SLOT:[0-9]+]](%esp)
+; X86-32: calll get_val
+; X86-64: movl %eax, [[SPILL_SLOT:[0-9]+]](%rsp)
+; X86-64: callq get_val
+
+  %setjmp_result = invoke i1 @setjmp() returns_twice
+      to label %cont unwind label %lpad
+; X86-32: calll setjmp
+; X86-64: callq setjmp
+
+cont:
+  br i1 %setjmp_result, label %second, label %first
+
+lpad:
+  %lp = landingpad { i8*, i32 } personality void ()* @personality cleanup
+  unreachable
+
+first:
+  %b1 = call i32 @get_val()
+  %b2 = call i32 @get_val()
+  %b3 = call i32 @get_val()
+  %b4 = call i32 @get_val()
+  %b5 = call i32 @get_val()
+  %b6 = call i32 @get_val()
+  %b7 = call i32 @get_val()
+  %b8 = call i32 @get_val()
+  call void @use_val(i32 %b1)
+  call void @use_val(i32 %b2)
+  call void @use_val(i32 %b3)
+  call void @use_val(i32 %b4)
+  call void @use_val(i32 %b5)
+  call void @use_val(i32 %b6)
+  call void @use_val(i32 %b7)
+  call void @use_val(i32 %b8)
+  call void @longjmp()
+  unreachable
+; X86-32-NOT: movl {{.*}}, [[SPILL_SLOT]](%esp)
+; X86-64-NOT: movl {{.*}}, [[SPILL_SLOT]](%rsp)
+
+second:
+  call void @use_val(i32 %a1)
+  call void @use_val(i32 %a2)
+  call void @use_val(i32 %a3)
+  call void @use_val(i32 %a4)
+  call void @use_val(i32 %a5)
+  call void @use_val(i32 %a6)
+  call void @use_val(i32 %a7)
+  call void @use_val(i32 %a8)
+  ret void
+}
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