[WebAssembly] Don't analyze branches after CFGStackify

Summary:
`WebAssembly::analyzeBranch` now does not analyze anything if the
function is CFG stackified. We were previously doing similar things by
checking if a branch's operand is whether an integer or an MBB, but this
failed to bail out when a BB did not have any terminators.

Consider this case:
```
bb0:
  try $label0
  call @foo    // unwinds to %ehpad
bb1:
  ...
  br $label0   // jumps to %cont. can be deleted
ehpad:
  catch
  ...
cont:
  end_try
```
Here `br $label0` will be deleted in CFGStackify's
`removeUnnecessaryInstrs` function, because we jump to the %cont block
even without the branch. But in this case, MachineVerifier fails to
verify this, because `ehpad` is not a successor of `bb1` even if `bb1`
does not have any terminators. MachineVerifier incorrectly thinks `bb1`
falls through to the next block.

This pass now consistently rejects all analysis after CFGStackify
whether a BB has terminators or not, also making the MachineVerifier
work. (MachineVerifier does not try to verify relationships between BBs
if `analyzeBranch` fails, the behavior we want after CFGStackify.)

This also adds a new option `-wasm-disable-ehpad-sort` for testing. This
option helps create the sorted order we want to test, and without the
fix in this patch, the tests in cfg-stackify-eh.ll fail at
MachineVerifier with `-wasm-disable-ehpad-sort`.

Reviewers: dschuff

Subscribers: sunfish, sbc100, jgravelle-google, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D59740

llvm-svn: 357015

3 files changed, 28 insertions, 21 deletions

diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyCFGSort.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyCFGSort.cpp
index 98bdfafef52..4c5d0192fc2 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyCFGSort.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyCFGSort.cpp
@@ -34,6 +34,14 @@ using namespace llvm;
 
 #define DEBUG_TYPE "wasm-cfg-sort"
 
+// Option to disable EH pad first sorting. Only for testing unwind destination
+// mismatches in CFGStackify.
+static cl::opt<bool> WasmDisableEHPadSort(
+    "wasm-disable-ehpad-sort", cl::ReallyHidden,
+    cl::desc(
+        "WebAssembly: Disable EH pad-first sort order. Testing purpose only."),
+    cl::init(false));
+
 namespace {
 
 // Wrapper for loops and exceptions
@@ -187,10 +195,12 @@ namespace {
 struct CompareBlockNumbers {
   bool operator()(const MachineBasicBlock *A,
                   const MachineBasicBlock *B) const {
-    if (A->isEHPad() && !B->isEHPad())
-      return false;
-    if (!A->isEHPad() && B->isEHPad())
-      return true;
+    if (!WasmDisableEHPadSort) {
+      if (A->isEHPad() && !B->isEHPad())
+        return false;
+      if (!A->isEHPad() && B->isEHPad())
+        return true;
+    }
 
     return A->getNumber() > B->getNumber();
   }
@@ -199,11 +209,12 @@ struct CompareBlockNumbers {
 struct CompareBlockNumbersBackwards {
   bool operator()(const MachineBasicBlock *A,
                   const MachineBasicBlock *B) const {
-    // We give a higher priority to an EH pad
-    if (A->isEHPad() && !B->isEHPad())
-      return false;
-    if (!A->isEHPad() && B->isEHPad())
-      return true;
+    if (!WasmDisableEHPadSort) {
+      if (A->isEHPad() && !B->isEHPad())
+        return false;
+      if (!A->isEHPad() && B->isEHPad())
+        return true;
+    }
 
     return A->getNumber() < B->getNumber();
   }
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyInstrInfo.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyInstrInfo.cpp
index a7c120963e0..3f5aba087f0 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyInstrInfo.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyInstrInfo.cpp
@@ -101,6 +101,13 @@ bool WebAssemblyInstrInfo::analyzeBranch(MachineBasicBlock &MBB,
                                          MachineBasicBlock *&FBB,
                                          SmallVectorImpl<MachineOperand> &Cond,
                                          bool /*AllowModify*/) const {
+  const auto &MFI = *MBB.getParent()->getInfo<WebAssemblyFunctionInfo>();
+  // WebAssembly has control flow that doesn't have explicit branches or direct
+  // fallthrough (e.g. try/catch), which can't be modeled by analyzeBranch. It
+  // is created after CFGStackify.
+  if (MFI.isCFGStackified())
+    return true;
+
   bool HaveCond = false;
   for (MachineInstr &MI : MBB.terminators()) {
     switch (MI.getOpcode()) {
@@ -110,9 +117,6 @@ bool WebAssemblyInstrInfo::analyzeBranch(MachineBasicBlock &MBB,
     case WebAssembly::BR_IF:
       if (HaveCond)
         return true;
-      // If we're running after CFGStackify, we can't optimize further.
-      if (!MI.getOperand(0).isMBB())
-        return true;
       Cond.push_back(MachineOperand::CreateImm(true));
       Cond.push_back(MI.getOperand(1));
       TBB = MI.getOperand(0).getMBB();
@@ -121,18 +125,12 @@ bool WebAssemblyInstrInfo::analyzeBranch(MachineBasicBlock &MBB,
     case WebAssembly::BR_UNLESS:
       if (HaveCond)
         return true;
-      // If we're running after CFGStackify, we can't optimize further.
-      if (!MI.getOperand(0).isMBB())
-        return true;
       Cond.push_back(MachineOperand::CreateImm(false));
       Cond.push_back(MI.getOperand(1));
       TBB = MI.getOperand(0).getMBB();
       HaveCond = true;
       break;
     case WebAssembly::BR:
-      // If we're running after CFGStackify, we can't optimize further.
-      if (!MI.getOperand(0).isMBB())
-        return true;
       if (!HaveCond)
         TBB = MI.getOperand(0).getMBB();
       else
@@ -141,9 +139,6 @@ bool WebAssemblyInstrInfo::analyzeBranch(MachineBasicBlock &MBB,
     case WebAssembly::BR_ON_EXN:
       if (HaveCond)
         return true;
-      // If we're running after CFGStackify, we can't optimize further.
-      if (!MI.getOperand(0).isMBB())
-        return true;
       Cond.push_back(MachineOperand::CreateImm(true));
       Cond.push_back(MI.getOperand(2));
       TBB = MI.getOperand(0).getMBB();
diff --git a/llvm/test/CodeGen/WebAssembly/cfg-stackify-eh.ll b/llvm/test/CodeGen/WebAssembly/cfg-stackify-eh.ll
index a93babedd13..f11c4ff2367 100644
--- a/llvm/test/CodeGen/WebAssembly/cfg-stackify-eh.ll
+++ b/llvm/test/CodeGen/WebAssembly/cfg-stackify-eh.ll
@@ -1,5 +1,6 @@
 ; 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
 
 target datalayout = "e-m:e-p:32:32-i64:64-n32:64-S128"
 target triple = "wasm32-unknown-unknown"