[llvm] c93b955 - [WebAssembly] Remove more unnecessary brs in CFGStackify
Heejin Ahn via llvm-commits
llvm-commits at lists.llvm.org
Tue Jan 12 01:18:32 PST 2021
Author: Heejin Ahn
Date: 2021-01-12T01:18:10-08:00
New Revision: c93b95593907c28cbcfde3d8266801587e110b42
URL: https://github.com/llvm/llvm-project/commit/c93b95593907c28cbcfde3d8266801587e110b42
DIFF: https://github.com/llvm/llvm-project/commit/c93b95593907c28cbcfde3d8266801587e110b42.diff
LOG: [WebAssembly] Remove more unnecessary brs in CFGStackify
After placing markers, we removed some unnecessary branches, but it only
handled the simplest case. This makes more unnecessary branches to be
removed.
Reviewed By: dschuff, tlively
Differential Revision: https://reviews.llvm.org/D94047
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 9a6d8df8bdca..a8e0c3efea0e 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyCFGStackify.cpp
@@ -637,11 +637,32 @@ void WebAssemblyCFGStackify::removeUnnecessaryInstrs(MachineFunction &MF) {
// try
// ...
// br bb2 <- Not necessary
- // bb1:
+ // bb1 (ehpad):
// catch
// ...
- // bb2:
+ // bb2: <- Continuation BB
// end
+ //
+ // A more involved case: When the BB where 'end' is located is an another EH
+ // pad, the Cont (= continuation) BB is that EH pad's 'end' BB. For example,
+ // bb0:
+ // try
+ // try
+ // ...
+ // br bb3 <- Not necessary
+ // bb1 (ehpad):
+ // catch
+ // bb2 (ehpad):
+ // end
+ // catch
+ // ...
+ // bb3: <- Continuation BB
+ // end
+ //
+ // When the EH pad at hand is bb1, its matching end_try is in bb2. But it is
+ // another EH pad, so bb0's continuation BB becomes bb3. So 'br bb3' in the
+ // code can be deleted. This is why we run 'while' until 'Cont' is not an EH
+ // pad.
for (auto &MBB : MF) {
if (!MBB.isEHPad())
continue;
@@ -649,7 +670,14 @@ void WebAssemblyCFGStackify::removeUnnecessaryInstrs(MachineFunction &MF) {
MachineBasicBlock *TBB = nullptr, *FBB = nullptr;
SmallVector<MachineOperand, 4> Cond;
MachineBasicBlock *EHPadLayoutPred = MBB.getPrevNode();
- MachineBasicBlock *Cont = BeginToEnd[EHPadToTry[&MBB]]->getParent();
+
+ MachineBasicBlock *Cont = &MBB;
+ while (Cont->isEHPad()) {
+ MachineInstr *Try = EHPadToTry[Cont];
+ MachineInstr *EndTry = BeginToEnd[Try];
+ Cont = EndTry->getParent();
+ }
+
bool Analyzable = !TII.analyzeBranch(*EHPadLayoutPred, TBB, FBB, Cond);
// This condition means either
// 1. This BB ends with a single unconditional branch whose destinaion is
diff --git a/llvm/test/CodeGen/WebAssembly/cfg-stackify-eh.ll b/llvm/test/CodeGen/WebAssembly/cfg-stackify-eh.ll
index 3079d9e15b82..209aaea2aaf6 100644
--- a/llvm/test/CodeGen/WebAssembly/cfg-stackify-eh.ll
+++ b/llvm/test/CodeGen/WebAssembly/cfg-stackify-eh.ll
@@ -935,7 +935,18 @@ last: ; preds = %bb0
}
; Tests if CFGStackify's removeUnnecessaryInstrs() removes unnecessary branches
-; correctly.
+; correctly. The code is in the form below, where 'br' is unnecessary because
+; after running the 'try' body the control flow will fall through to bb2 anyway.
+
+; bb0:
+; try
+; ...
+; br bb2 <- Not necessary
+; bb1 (ehpad):
+; catch
+; ...
+; bb2: <- Continuation BB
+; end
; CHECK-LABEL: test17
define void @test17(i32 %n) personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
entry:
@@ -974,17 +985,91 @@ try.cont: ; preds = %catch.start, %for.e
ret void
}
+; void foo();
+; void test18() {
+; try {
+; foo();
+; try {
+; foo();
+; } catch (...) {
+; }
+; } catch (...) {
+; }
+; }
+;
+; This tests whether the 'br' can be removed in code in the form as follows.
+; Here 'br' is inside an inner try, whose 'end' is in another EH pad. In this
+; case, after running an inner try body, the control flow should fall through to
+; bb3, so the 'br' in the code is unnecessary.
+
+; bb0:
+; try
+; try
+; ...
+; br bb3 <- Not necessary
+; bb1:
+; catch
+; bb2:
+; end_try
+; catch
+; ...
+; bb3: <- Continuation BB
+; end
+;
+; CHECK-LABEL: test18
+define void @test18() personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
+; CHECK: call foo
+entry:
+ invoke void @foo()
+ to label %invoke.cont unwind label %catch.dispatch3
+
+; CHECK: call foo
+; CHECK-NOT: br
+invoke.cont: ; preds = %entry
+ invoke void @foo()
+ to label %try.cont8 unwind label %catch.dispatch
+
+catch.dispatch: ; preds = %invoke.cont
+ %0 = catchswitch within none [label %catch.start] unwind label %catch.dispatch3
+
+; CHECK: catch
+catch.start: ; preds = %catch.dispatch
+ %1 = catchpad within %0 [i8* null]
+ %2 = call i8* @llvm.wasm.get.exception(token %1)
+ %3 = call i32 @llvm.wasm.get.ehselector(token %1)
+ %4 = call i8* @__cxa_begin_catch(i8* %2) #2 [ "funclet"(token %1) ]
+ invoke void @__cxa_end_catch() [ "funclet"(token %1) ]
+ to label %invoke.cont2 unwind label %catch.dispatch3
+
+catch.dispatch3: ; preds = %catch.start, %catch.dispatch, %entry
+ %5 = catchswitch within none [label %catch.start4] unwind to caller
+
+catch.start4: ; preds = %catch.dispatch3
+ %6 = catchpad within %5 [i8* null]
+ %7 = call i8* @llvm.wasm.get.exception(token %6)
+ %8 = call i32 @llvm.wasm.get.ehselector(token %6)
+ %9 = call i8* @__cxa_begin_catch(i8* %7) #2 [ "funclet"(token %6) ]
+ call void @__cxa_end_catch() [ "funclet"(token %6) ]
+ catchret from %6 to label %try.cont8
+
+try.cont8: ; preds = %invoke.cont, %invoke.cont2, %catch.start4
+ ret void
+
+invoke.cont2: ; preds = %catch.start
+ catchret from %1 to label %try.cont8
+}
+
; Here an exception is semantically contained in a loop. 'ehcleanup' BB belongs
; to the exception, but does not belong to the loop (because it does not have a
; path back to the loop header), and is placed after the loop latch block
; 'invoke.cont' intentionally. This tests if 'end_loop' marker is placed
; correctly not right after 'invoke.cont' part but after 'ehcleanup' part,
-; NOSORT-LABEL: test18
+; NOSORT-LABEL: test19
; NOSORT: loop
; NOSORT: try
; NOSORT: end_try
; NOSORT: end_loop
-define void @test18(i32 %n) personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
+define void @test19(i32 %n) personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
entry:
br label %while.cond
@@ -1029,14 +1114,14 @@ while.end: ; preds = %while.body, %while.
; before its corresponding `catch`, because both `try` and `catch` body should
; satisfy the return type requirements.
-; NOSORT-LABEL: test19
+; NOSORT-LABEL: test20
; NOSORT: try i32
; NOSORT: loop i32
; NOSORT: end_loop
; NOSORT: catch
; NOSORT: end_try
; NOSORT-NEXT: end_function
-define i32 @test19(i32 %n) personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
+define i32 @test20(i32 %n) personality i8* bitcast (i32 (...)* @__gxx_wasm_personality_v0 to i8*) {
entry:
%t = alloca %class.Object, align 1
br label %for.cond
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