[PATCH] D150033: fix stack probe lowering for x86_intrcc

[Tom Dohrmann via Phabricator via llvm-commits]

Freax13 updated this revision to Diff 520157.
Freax13 added a comment.

Instead of handling multiple STACKALLOC_W_PROBING machine instructions, we now just hard-code the stack update for x86_intrcc with an error code to `push rax`.


CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D150033/new/

https://reviews.llvm.org/D150033

Files:
  llvm/lib/Target/X86/X86FrameLowering.cpp
  llvm/test/CodeGen/X86/x86-64-intrcc.ll


Index: llvm/test/CodeGen/X86/x86-64-intrcc.ll
===================================================================
--- llvm/test/CodeGen/X86/x86-64-intrcc.ll
+++ llvm/test/CodeGen/X86/x86-64-intrcc.ll
@@ -174,5 +174,22 @@
   ret void
 }
 
+define x86_intrcc void @test_stack_allocation(ptr byval(%struct.interrupt_frame) %frame, i64 %err) #1 {
+  ; CHECK-LABEL: test_stack_allocation:
+  ; CHECK: # %bb.0: # %entry
+  
+  ;; Ensure that STACKALLOC_W_PROBING isn't emitted.
+  ; CHECK-NOT: # fixed size alloca with probing
+  ;; Ensure that stack space is allocated. 
+  ; CHECK: subq    $280, %rsp
+entry:
+  %some_allocation = alloca i64
+  ;; Call a un-inlineable function to ensure the allocation isn't put in the red zone.
+  call void @external_function(ptr %some_allocation)
+  ret void
+}
+
+declare void @external_function(ptr)
 
 attributes #0 = { nounwind "frame-pointer"="all" }
+attributes #1 = { nounwind "probe-stack"="inline-asm" }
Index: llvm/lib/Target/X86/X86FrameLowering.cpp
===================================================================
--- llvm/lib/Target/X86/X86FrameLowering.cpp
+++ llvm/lib/Target/X86/X86FrameLowering.cpp
@@ -1644,7 +1644,19 @@
       Fn.arg_size() == 2) {
     StackSize += 8;
     MFI.setStackSize(StackSize);
-    emitSPUpdate(MBB, MBBI, DL, -8, /*InEpilogue=*/false);
+
+    // Update the stack pointer by pushing a register. This is the instruction
+    // emitted that would be end up being emitted by a call to `emitSPUpdate`.
+    // Hard-coding the update to a push avoids emitting a second
+    // `STACKALLOC_W_PROBING` instruction in the save block: We know that stack
+    // probing isn't needed anyways for an 8-byte update.
+    // Pushing a register leaves us in a similar situation to a regular
+    // function call where we know that the address at (rsp-8) is writeable.
+    // That way we avoid any off-by-ones with stack probing for additional
+    // stack pointer updates later on.
+    BuildMI(MBB, MBBI, DL, TII.get(X86::PUSH64r))
+        .addReg(X86::RAX, RegState::Undef)
+        .setMIFlag(MachineInstr::FrameSetup);
   }
 
   // If this is x86-64 and the Red Zone is not disabled, if we are a leaf


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D150033.520157.patch
Type: text/x-patch
Size: 2178 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20230507/3f562bc5/attachment.bin>