[PATCH] D51114: [WebAssembly] Don't write SP back when prolog is generated only for EH

[Derek Schuff via Phabricator via llvm-commits]

dschuff added inline comments.


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Comment at: lib/Target/WebAssembly/WebAssemblyEHRestoreStackPointer.cpp:73
+    // Here it is safe to assume that SP32 holds the latest value of
+    // __stack_poiner, because the only exception for this case is when a
+    // function uses the red zone, but that only happens with leaf functions,
----------------
__stack_pointer


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Comment at: lib/Target/WebAssembly/WebAssemblyEHRestoreStackPointer.cpp:75
+    // function uses the red zone, but that only happens with leaf functions,
+    // and leaf functions can't catch exceptions anyway.
     auto InsertPos = MBB.begin();
----------------
can't leaf functions have try/catch blocks, even if there are no calls? I think the real issue is that leaf functions do not to restore the stack pointer on catch, because it won't have been updated by any callees.


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Comment at: lib/Target/WebAssembly/WebAssemblyFrameLowering.cpp:115
+  bool NeedsSPOnlyForEH = !MFI.getStackSize() && !MFI.adjustsStack() &&
+                          !hasFP(MF) && needsPrologForEH(MF);
+  bool CanUseRedZone = MFI.getStackSize() <= RedZoneSize && !MFI.hasCalls() &&
----------------
Another possible way:
`bool NeedsSPForLocalFrame = MFI.getStackSize() || !MFI.adjustsStack() || hasFP(MF);`

which would avoid so many nots...

Actually, even better may be to turn `NeedsSPForLocalFrame()` into a function (that can be called by `needsSP()`). Then you can reuse it here instead of duplicating the logic?



Repository:
  rL LLVM

https://reviews.llvm.org/D51114