[PATCH] D46777: [ARM] Back up R4 and LR if calling the stack probe function

[Martin Storsjö via Phabricator via llvm-commits]

mstorsjo updated this revision to Diff 146463.
mstorsjo added a comment.

Simplified the estimate, elaborated the comment a little.


https://reviews.llvm.org/D46777

Files:
  lib/Target/ARM/ARMFrameLowering.cpp
  test/CodeGen/ARM/Windows/chkstk-movw-movt-isel.ll


Index: test/CodeGen/ARM/Windows/chkstk-movw-movt-isel.ll
===================================================================
--- test/CodeGen/ARM/Windows/chkstk-movw-movt-isel.ll
+++ test/CodeGen/ARM/Windows/chkstk-movw-movt-isel.ll
@@ -18,7 +18,7 @@
 }
 
 ; CHECK-LABEL: isel
-; CHECK: push {r4, r5}
+; CHECK: push {r4, r5, r6, lr}
 ; CHECK: movw r12, #0
 ; CHECK: movt r12, #0
 ; CHECK: movw r4, #{{\d*}}
Index: lib/Target/ARM/ARMFrameLowering.cpp
===================================================================
--- lib/Target/ARM/ARMFrameLowering.cpp
+++ lib/Target/ARM/ARMFrameLowering.cpp
@@ -1616,9 +1616,20 @@
   // since it's not always possible to restore sp from fp in a single
   // instruction.
   // FIXME: It will be better just to find spare register here.
-  if (AFI->isThumb2Function() &&
-      (MFI.hasVarSizedObjects() || RegInfo->needsStackRealignment(MF)))
-    SavedRegs.set(ARM::R4);
+  if (AFI->isThumb2Function()) {
+    if (MFI.hasVarSizedObjects() || RegInfo->needsStackRealignment(MF))
+      SavedRegs.set(ARM::R4);
+
+    // If a stack probe will be emitted, spill R4 and LR, since they are
+    // clobbered by the stack probe call.
+    // This estimate should be a safe, conservative estimate. The actual
+    // stack probe is enabled based on the size of the local objects;
+    // this estimate also includes the varargs store size.
+    if (STI.isTargetWindows() && WindowsRequiresStackProbe(MF, MFI.estimateStackSize(MF))) {
+      SavedRegs.set(ARM::R4);
+      SavedRegs.set(ARM::LR);
+    }
+  }
 
   if (AFI->isThumb1OnlyFunction()) {
     // Spill LR if Thumb1 function uses variable length argument lists.


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