[llvm] ba40896 - [WebAssembly] Fix try placement in fixing unwind mismatches
Heejin Ahn via llvm-commits
llvm-commits at lists.llvm.org
Mon Apr 13 15:53:56 PDT 2020
Author: Heejin Ahn
Date: 2020-04-13T15:50:01-07:00
New Revision: ba40896f99f2996c20d68f45b0151309406935a5
URL: https://github.com/llvm/llvm-project/commit/ba40896f99f2996c20d68f45b0151309406935a5
DIFF: https://github.com/llvm/llvm-project/commit/ba40896f99f2996c20d68f45b0151309406935a5.diff
LOG: [WebAssembly] Fix try placement in fixing unwind mismatches
Summary:
In CFGStackify, `fixUnwindMismatches` function fixes unwind destination
mismatches created by `try` marker placement. For example,
```
try
...
call @qux ;; This should throw to the caller!
catch
...
end
```
When `call @qux` is supposed to throw to the caller, it is possible that
it is wrapped inside a `catch` so in case it throws it ends up unwinding
there incorrectly. (Also it is possible `call @qux` is supposed to
unwind to another `catch` within the same function.)
To fix this, we wrap this inner `call @qux` with a nested
`try`-`catch`-`end` sequence, and within the nested `catch` body, branch
to the right destination:
```
block $l0
try
...
try ;; new nested try
call @qux
catch ;; new nested catch
local.set n ;; store exnref to a local
br $l0
end
catch
...
end
end
local.get n ;; retrieve exnref back
rethrow ;; rethrow to the caller
```
The previous algorithm placed the nested `try` right before the `call`.
But it is possible that there are stackified instructions before the
call from which the call takes arguments.
```
try
...
i32.const 5
call @qux ;; This should throw to the caller!
catch
...
end
```
In this case we have to place `try` before those stackified
instructions.
```
block $l0
try
...
try ;; this should go *before* 'i32.const 5'
i32.const 5
call @qux
catch
local.set n
br $l0
end
catch
...
end
end
local.get n
rethrow
```
We correctly handle this in the first normal `try` placement phase
(`placeTryMarker` function), but failed to handle this in this
`fixUnwindMismatches`.
Reviewers: dschuff
Subscribers: sbc100, jgravelle-google, hiraditya, sunfish, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D77950
Added:
Modified:
llvm/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp
llvm/test/CodeGen/WebAssembly/cfg-stackify-eh.ll
Removed:
################################################################################
diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp
index 7e867edaaa27..989c3da10911 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp
@@ -1109,6 +1109,9 @@ bool WebAssemblyCFGStackify::fixUnwindMismatches(MachineFunction &MF) {
MachineInstr *RangeBegin = nullptr, *RangeEnd = nullptr;
std::tie(RangeBegin, RangeEnd) = Range;
auto *MBB = RangeBegin->getParent();
+ // Store the first function call from this range, because RangeBegin can
+ // be moved to point EH_LABEL before the call
+ MachineInstr *RangeBeginCall = RangeBegin;
// Include possible EH_LABELs in the range
if (RangeBegin->getIterator() != MBB->begin() &&
@@ -1126,9 +1129,27 @@ bool WebAssemblyCFGStackify::fixUnwindMismatches(MachineFunction &MF) {
}
}
+ // Local expression tree before the first call of this range should go
+ // after the nested TRY.
+ SmallPtrSet<const MachineInstr *, 4> AfterSet;
+ AfterSet.insert(RangeBegin);
+ AfterSet.insert(RangeBeginCall);
+ for (auto I = MachineBasicBlock::iterator(RangeBeginCall),
+ E = MBB->begin();
+ I != E; --I) {
+ if (std::prev(I)->isDebugInstr() || std::prev(I)->isPosition())
+ continue;
+ if (WebAssembly::isChild(*std::prev(I), MFI))
+ AfterSet.insert(&*std::prev(I));
+ else
+ break;
+ }
+
// Create the nested try instruction.
+ auto InsertPos = getLatestInsertPos(
+ MBB, SmallPtrSet<const MachineInstr *, 4>(), AfterSet);
MachineInstr *NestedTry =
- BuildMI(*MBB, *RangeBegin, RangeBegin->getDebugLoc(),
+ BuildMI(*MBB, InsertPos, RangeBegin->getDebugLoc(),
TII.get(WebAssembly::TRY))
.addImm(int64_t(WebAssembly::BlockType::Void));
diff --git a/llvm/test/CodeGen/WebAssembly/cfg-stackify-eh.ll b/llvm/test/CodeGen/WebAssembly/cfg-stackify-eh.ll
index a4d8537343ca..5cbff5d0bb62 100644
--- a/llvm/test/CodeGen/WebAssembly/cfg-stackify-eh.ll
+++ b/llvm/test/CodeGen/WebAssembly/cfg-stackify-eh.ll
@@ -483,16 +483,65 @@ try.cont: ; preds = %catch.start0
ret void
}
+; Similar situation as @test6. Here 'call @qux''s original unwind destination
+; was the caller, but after control flow linearization, their unwind destination
+; incorrectly becomes another catch within the function. We fix this by wrapping
+; the call with a nested try/catch/end_try and branching to the right
+; destination, from which we rethrow the exception to the caller.
+
+; Because 'call @qux' pops an argument pushed by 'i32.const 5' from stack, the
+; nested 'try' should be placed before `i32.const 5', not between 'i32.const 5'
+; and 'call @qux'.
+
+; NOSORT-LABEL: test7
+; NOSORT: try
+; NOSORT: call foo
+; --- Nested try/catch/end_try starts
+; NOSORT: try
+; NOSORT-NEXT: i32.const $push{{[0-9]+}}=, 5
+; NOSORT-NEXT: call ${{[0-9]+}}=, qux
+; NOSORT: catch $[[REG:[0-9]+]]=
+; NOSORT: br 1 # 1: down to label37
+; NOSORT: end_try
+; --- Nested try/catch/end_try ends
+; NOSORT: return
+; NOSORT: catch $drop= # catch19:
+; NOSORT: return
+; NOSORT: end_try # label37:
+; NOSORT: rethrow $[[REG]] # to caller
+
+define i32 @test7() personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
+bb0:
+ invoke void @foo()
+ to label %bb1 unwind label %catch.dispatch0
+
+bb1: ; preds = %bb0
+ %0 = call i32 @qux(i32 5)
+ ret i32 %0
+
+catch.dispatch0: ; preds = %bb0
+ %1 = catchswitch within none [label %catch.start0] unwind to caller
+
+catch.start0: ; preds = %catch.dispatch0
+ %2 = catchpad within %1 [i8* null]
+ %3 = call i8* @llvm.wasm.get.exception(token %2)
+ %j = call i32 @llvm.wasm.get.ehselector(token %2)
+ catchret from %2 to label %try.cont
+
+try.cont: ; preds = %catch.start0
+ ret i32 0
+}
+
; If not for the unwind destination mismatch, the LOOP marker here would have an
; i32 signature. But because we add a rethrow instruction at the end of the
; appendix block, now the LOOP marker does not have a signature (= has a void
; signature). Here the two calls two 'bar' are supposed to throw up to the
; caller, but incorrectly unwind to 'catch19' after linearizing the CFG.
-; NOSORT-LABEL: test7
+; NOSORT-LABEL: test8
; NOSORT: block
; NOSORT-NOT: loop i32
-; NOSORT: loop # label38:
+; NOSORT: loop # label40:
; NOSORT: try
; NOSORT: call foo
; --- Nested try/catch/end_try starts
@@ -500,18 +549,18 @@ try.cont: ; preds = %catch.start0
; NOSORT: call bar
; NOSORT: call bar
; NOSORT: catch $[[REG:[0-9]+]]=
-; NOSORT: br 1 # 1: down to label39
+; NOSORT: br 1 # 1: down to label41
; NOSORT: end_try
; --- Nested try/catch/end_try ends
; NOSORT: return {{.*}}
-; NOSORT: catch $drop= # catch19:
-; NOSORT: br 1 # 1: up to label38
-; NOSORT: end_try # label39:
+; NOSORT: catch $drop= # catch21:
+; NOSORT: br 1 # 1: up to label40
+; NOSORT: end_try # label41:
; NOSORT: end_loop
; NOSORT: end_block
; NOSORT: rethrow $[[REG]] # to caller
-define i32 @test7(i32* %p) personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
+define i32 @test8(i32* %p) personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
entry:
store volatile i32 0, i32* %p
br label %loop
@@ -545,7 +594,7 @@ try.cont: ; preds = %catch.start
; - A may-throw instruction unwinds to an incorrect EH pad after linearizing the
; CFG, when it is supposed to unwind to the caller.
-; NOSORT-LABEL: test8
+; NOSORT-LABEL: test9
; NOSORT: block
; NOSORT: block
; NOSORT: try
@@ -555,40 +604,40 @@ try.cont: ; preds = %catch.start
; NOSORT: try
; NOSORT: call bar
; NOSORT: catch $[[REG0:[0-9]+]]=
-; NOSORT: br 2 # 2: down to label43
+; NOSORT: br 2 # 2: down to label45
; NOSORT: end_try
; --- Nested try/catch/end_try ends
-; NOSORT: br 2 # 2: down to label42
+; NOSORT: br 2 # 2: down to label44
; NOSORT: catch {{.*}}
; NOSORT: block i32
-; NOSORT: br_on_exn 0, {{.*}} # 0: down to label46
+; NOSORT: br_on_exn 0, {{.*}} # 0: down to label48
; --- Nested try/catch/end_try starts
; NOSORT: try
-; NOSORT: rethrow {{.*}} # down to catch24
-; NOSORT: catch $[[REG1:[0-9]+]]= # catch24:
-; NOSORT: br 5 # 5: down to label41
+; NOSORT: rethrow {{.*}} # down to catch26
+; NOSORT: catch $[[REG1:[0-9]+]]= # catch26:
+; NOSORT: br 5 # 5: down to label43
; NOSORT: end_try
; --- Nested try/catch/end_try ends
-; NOSORT: end_block # label46:
+; NOSORT: end_block # label48:
; NOSORT: call $drop=, __cxa_begin_catch
; --- Nested try/catch/end_try starts
; NOSORT: try
; NOSORT: call __cxa_end_catch
; NOSORT: catch $[[REG1]]=
-; NOSORT: br 4 # 4: down to label41
+; NOSORT: br 4 # 4: down to label43
; NOSORT: end_try
; --- Nested try/catch/end_try ends
-; NOSORT: br 2 # 2: down to label42
+; NOSORT: br 2 # 2: down to label44
; NOSORT: end_try
; NOSORT: catch $[[REG0]]=
-; NOSORT: end_try # label43:
+; NOSORT: end_try # label45:
; NOSORT: call $drop=, __cxa_begin_catch
; NOSORT: call __cxa_end_catch
-; NOSORT: end_block # label42:
+; NOSORT: end_block # label44:
; NOSORT: return
-; NOSORT: end_block # label41:
+; NOSORT: end_block # label43:
; NOSORT: rethrow $[[REG1]] # to caller
-define void @test8() personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
+define void @test9() personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
bb0:
invoke void @foo()
to label %bb1 unwind label %catch.dispatch0
@@ -638,7 +687,7 @@ try.cont: ; preds = %catch.start1, %catc
; NOOPT: call foo
; NOOPT: end_block
; NOOPT: return
-define void @test9(i32 %arg) personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
+define void @test10(i32 %arg) personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
entry:
%tobool = icmp ne i32 %arg, 0
br i1 %tobool, label %if.then, label %if.end
@@ -675,7 +724,7 @@ if.end: ; preds = %cont, %catch.start,
; invoke.cont BB fall within try~end_try, but they shouldn't cause crashes or
; unwinding destination mismatches in CFGStackify.
-; NOSORT-LABEL: test10
+; NOSORT-LABEL: test11
; NOSORT: try
; NOSORT: call foo
; NOSORT: call {{.*}} memcpy
@@ -685,7 +734,7 @@ if.end: ; preds = %cont, %catch.start,
; NOSORT: catch
; NOSORT: rethrow
; NOSORT: end_try
-define void @test10(i8* %a, i8* %b) personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
+define void @test11(i8* %a, i8* %b) personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
entry:
%o = alloca %class.Object, align 1
invoke void @foo()
@@ -709,11 +758,11 @@ ehcleanup: ; preds = %entry
; 'nothrow_i32' and 'fun', because the return value of 'nothrow_i32' is
; stackified and pushed onto the stack to be consumed by the call to 'fun'.
-; CHECK-LABEL: test11
+; CHECK-LABEL: test12
; CHECK: try
; CHECK: call $push{{.*}}=, nothrow_i32
; CHECK: call fun, $pop{{.*}}
-define void @test11() personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
+define void @test12() personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
entry:
%call = call i32 @nothrow_i32()
invoke void @fun(i32 %call)
@@ -734,7 +783,7 @@ terminate: ; preds = %entry
; This crashed on debug mode (= when NDEBUG is not defined) when the logic for
; computing the innermost region was not correct, in which a loop region
; contains an exception region. This should pass CFGSort without crashing.
-define void @test12() personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
+define void @test13() personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
entry:
%e = alloca %class.MyClass, align 4
br label %for.cond
@@ -802,11 +851,12 @@ terminate7: ; preds = %ehcleanup
}
; Check if the unwind destination mismatch stats are correct
-; NOSORT-STAT: 14 wasm-cfg-stackify - Number of EH pad unwind mismatches found
+; NOSORT-STAT: 15 wasm-cfg-stackify - Number of EH pad unwind mismatches found
declare void @foo()
declare void @bar()
declare i32 @baz()
+declare i32 @qux(i32)
declare void @quux(i32)
declare void @fun(i32)
; Function Attrs: nounwind
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