[llvm] r369978 - [WebAssembly] Fix SSA rebuilding in SjLj transformation

[Heejin Ahn via llvm-commits]

Author: aheejin
Date: Mon Aug 26 14:51:35 2019
New Revision: 369978

URL: http://llvm.org/viewvc/llvm-project?rev=369978&view=rev
Log:
[WebAssembly] Fix SSA rebuilding in SjLj transformation

Summary:
Previously we skipped uses within the same BB as a def when rebuilding
SSA after SjLj transformation. For example, before transformation,
```
for.cond:
  %0 = phi i32 [ %var, %for.inc ] ...
  %var = ...
  br label %for.inc

for.inc:                               ; preds = %for.cond
  call i32 @setjmp(...)
  br %for.cond
```

In this BB, %var should be defined in all paths from %for.inc to make %0
valid. In the input it was true; %for.inc's only predecessor was
%for.cond. But after SjLj transformation, it is possible that %for.inc
has other predecessors that are reachable without reaching %for.cond.
```
entry.split:
  ...
  br i1 %a, label %bb.1, label %for.inc

for.cond:
  %0 = phi i32 [ %var, %for.inc ] ...  ; Not valid!
  %var = ...
  br label %for.inc

for.inc:                               ; preds = %for.cond, %entry.split
  call i32 @setjmp(...)
  ...
  br %for.cond
```

In this case, we can't use %var in the `phi` instruction in %for.cond,
because %var is not defined in all paths through %for.inc (If the
control flow is %entry -> %entry.split -> %for.inc -> %for.cond, %var
has not been defined until we reach the `phi`). But the previous code
excluded users within the same BB, skipping instructions within the same
BB so they are not rewritten properly. User instructions within the same
BB also should be candidates for rewriting if they are _before_ the
original definition.

Fixes PR43097.

Reviewers: dschuff

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

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D66729

Modified:
    llvm/trunk/lib/Target/WebAssembly/WebAssemblyLowerEmscriptenEHSjLj.cpp
    llvm/trunk/test/CodeGen/WebAssembly/lower-em-sjlj.ll

Modified: llvm/trunk/lib/Target/WebAssembly/WebAssemblyLowerEmscriptenEHSjLj.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/WebAssembly/WebAssemblyLowerEmscriptenEHSjLj.cpp?rev=369978&r1=369977&r2=369978&view=diff
==============================================================================
--- llvm/trunk/lib/Target/WebAssembly/WebAssemblyLowerEmscriptenEHSjLj.cpp (original)
+++ llvm/trunk/lib/Target/WebAssembly/WebAssemblyLowerEmscriptenEHSjLj.cpp Mon Aug 26 14:51:35 2019
@@ -636,15 +636,12 @@ void WebAssemblyLowerEmscriptenEHSjLj::r
   SSAUpdater SSA;
   for (BasicBlock &BB : F) {
     for (Instruction &I : BB) {
+      SSA.Initialize(I.getType(), I.getName());
+      SSA.AddAvailableValue(&BB, &I);
       for (auto UI = I.use_begin(), UE = I.use_end(); UI != UE;) {
         Use &U = *UI;
         ++UI;
-        SSA.Initialize(I.getType(), I.getName());
-        SSA.AddAvailableValue(&BB, &I);
         auto *User = cast<Instruction>(U.getUser());
-        if (User->getParent() == &BB)
-          continue;
-
         if (auto *UserPN = dyn_cast<PHINode>(User))
           if (UserPN->getIncomingBlock(U) == &BB)
             continue;

Modified: llvm/trunk/test/CodeGen/WebAssembly/lower-em-sjlj.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/WebAssembly/lower-em-sjlj.ll?rev=369978&r1=369977&r2=369978&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/WebAssembly/lower-em-sjlj.ll (original)
+++ llvm/trunk/test/CodeGen/WebAssembly/lower-em-sjlj.ll Mon Aug 26 14:51:35 2019
@@ -226,6 +226,26 @@ entry:
   unreachable
 }
 
+; Tests if SSA rewrite works when a use and its def are within the same BB.
+define void @ssa_rewite_in_same_bb() {
+entry:
+  call void @foo()
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.inc, %entry
+  ; CHECK: %{{.*}} = phi i32 [ %var[[VARNO:.*]], %for.inc.split ]
+  %0 = phi i32 [ %var, %for.inc ], [ undef, %entry ]
+  %var = add i32 0, 0
+  br label %for.inc
+
+for.inc:                                          ; preds = %for.cond
+  %call5 = call i32 @setjmp(%struct.__jmp_buf_tag* undef) #0
+  br label %for.cond
+
+; CHECK: for.inc.split:
+  ; CHECK: %var[[VARNO]] = phi i32 [ %var, %for.inc ]
+}
+
 declare void @foo()
 ; Function Attrs: returns_twice
 declare i32 @setjmp(%struct.__jmp_buf_tag*) #0