[WebAssembly] Fix unwind mismatch stat computation

[aheejin]

Summary

There was a bug when computing the number of unwind destination
mismatches in CFGStackify. When there are many mismatched calls that
share the same (original) destination BB, they have to be counted
separately.

This also fixes a typo and runs fixUnwindMismatches only when the wasm
exception handling is enabled. This is to prevent unnecessary
computations and does not change behavior.

[aheejin]

Rebase onto D68553

[shchenz]

llvm/test/CodeGen/WebAssembly/cfg-stackify-eh.ll

706

This causes make check-llvm fail for release llc.

Need to add ; REQUIRES: asserts at the beginning?

[aheejin]

Thank you! Done in r374015.

llvm/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp

bool WebAssemblyCFGStackify::fixUnwindMismatches(MachineFunction &MF) {
   // can be wrapped together in one nested try scope. (In 1, this couldn't
   // happen, because may-throwing instruction there had an unwind destination,
   // i.e., it was an invoke before, and there could be only one invoke within a
   // BB.)
 
   SmallVector<const MachineBasicBlock *, 8> EHPadStack;
   // Range of intructions to be wrapped in a new nested try/catch
   using TryRange = std::pair<MachineInstr *, MachineInstr *>;
-  // In original CFG, <unwind destionation BB, a vector of try ranges>
+  // In original CFG, <unwind destination BB, a vector of try ranges>
   DenseMap<MachineBasicBlock *, SmallVector<TryRange, 4>> UnwindDestToTryRanges;
   // In new CFG, <destination to branch to, a vector of try ranges>
   DenseMap<MachineBasicBlock *, SmallVector<TryRange, 4>> BrDestToTryRanges;
   // In new CFG, <destination to branch to, register containing exnref>
   DenseMap<MachineBasicBlock *, unsigned> BrDestToExnReg;
 
   // Gather possibly throwing calls (i.e., previously invokes) whose current
   // unwind destination is not the same as the original CFG.
bool WebAssemblyCFGStackify::fixUnwindMismatches(MachineFunction &MF) {
   //   catch
   //   local.set n / drop
   // brdest:               (new)
   //   end_try             (hoisted from 'cont' BB)
   //   handler body        (taken from 'ehpad')
   // ...
   // cont:
   for (auto &P : UnwindDestToTryRanges) {
-    NumUnwindMismatches++;
+    NumUnwindMismatches += P.second.size();
 
     // This means the destination is the appendix BB, which was separately
     // handled above.
     if (!P.first)
       continue;
 
     MachineBasicBlock *EHPad = P.first;
 
if (MBB.isEHPad()) {
           MF.getFunction().hasPersonalityFn())
         placeTryMarker(MBB);
     } else {
       // Place the BLOCK for MBB if MBB is branched to from above.
       placeBlockMarker(MBB);
     }
   }
   // Fix mismatches in unwind destinations induced by linearizing the code.
+  if (MCAI->getExceptionHandlingType() == ExceptionHandling::Wasm &&
+      MF.getFunction().hasPersonalityFn())
     fixUnwindMismatches(MF);
 }
 
 void WebAssemblyCFGStackify::rewriteDepthImmediates(MachineFunction &MF) {
   // Now rewrite references to basic blocks to be depth immediates.
   SmallVector<const MachineBasicBlock *, 8> Stack;
   for (auto &MBB : reverse(MF)) {
     for (auto I = MBB.rbegin(), E = MBB.rend(); I != E; ++I) {
       MachineInstr &MI = *I;

llvm/test/CodeGen/WebAssembly/cfg-stackify-eh.ll

 ; RUN: llc < %s -disable-wasm-fallthrough-return-opt -wasm-disable-explicit-locals -wasm-keep-registers -disable-block-placement -verify-machineinstrs -fast-isel=false -machine-sink-split-probability-threshold=0 -cgp-freq-ratio-to-skip-merge=1000 -exception-model=wasm -mattr=+exception-handling | FileCheck %s
 ; RUN: llc < %s -O0 -disable-wasm-fallthrough-return-opt -wasm-disable-explicit-locals -wasm-keep-registers -verify-machineinstrs -exception-model=wasm -mattr=+exception-handling | FileCheck %s --check-prefix=NOOPT
 ; RUN: llc < %s -disable-wasm-fallthrough-return-opt -wasm-disable-explicit-locals -wasm-keep-registers -disable-block-placement -verify-machineinstrs -fast-isel=false -machine-sink-split-probability-threshold=0 -cgp-freq-ratio-to-skip-merge=1000 -exception-model=wasm -mattr=+exception-handling -wasm-disable-ehpad-sort | FileCheck %s --check-prefix=NOSORT
+; RUN: llc < %s -disable-wasm-fallthrough-return-opt -wasm-disable-explicit-locals -wasm-keep-registers -disable-block-placement -verify-machineinstrs -fast-isel=false -machine-sink-split-probability-threshold=0 -cgp-freq-ratio-to-skip-merge=1000 -exception-model=wasm -mattr=+exception-handling -wasm-disable-ehpad-sort -stats 2>&1 | FileCheck %s --check-prefix=NOSORT-STAT
 
 target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
 target triple = "wasm32-unknown-unknown"
 
 @_ZTIi = external constant i8*
 @_ZTId = external constant i8*
 
 ; Simple test case with two catch clauses
invoke.cont:                                      ; preds = %entry
   ret void
 
 ehcleanup:                                        ; preds = %entry
   %0 = cleanuppad within none []
   %call2 = call %class.Object* @_ZN6ObjectD2Ev(%class.Object* %o) #1 [ "funclet"(token %0) ]
   cleanupret from %0 unwind to caller
 }
 
+; Check if the unwind destination mismatch stats are correct
+; NOSORT-STAT: 11 wasm-cfg-stackify    - Number of EH pad unwind mismatches found
+
 declare void @foo()
 declare void @bar()
 declare i32 @baz()
 ; Function Attrs: nounwind
 declare void @nothrow(i32) #0
 ; Function Attrs: nounwind
 declare %class.Object* @_ZN6ObjectD2Ev(%class.Object* returned) #0
 declare i32 @__gxx_wasm_personality_v0(...)