[WebAssembly] Don't use setRequiresStructuredCFG(true).

While we still do want reducible control flow, the RequiresStructuredCFG
flag imposes more strict structure constraints than WebAssembly wants.
Unsetting this flag enables critical edge splitting and tail merging.

Also, disable TailDuplication explicitly, as it doesn't support virtual
registers, and was previously only disabled by the RequiresStructuredCFG
flag.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@261190 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/WebAssembly/WebAssemblyTargetMachine.cpp

@@ -58,9 +58,9 @@ WebAssemblyTargetMachine::WebAssemblyTargetMachine(
 
   initAsmInfo();
 
-  // We need a reducible CFG, so disable some optimizations which tend to
-  // introduce irreducibility.
-  setRequiresStructuredCFG(true);
+  // Note that we don't use setRequiresStructuredCFG(true). It disables
+  // optimizations than we're ok with, and want, such as critical edge
+  // splitting and tail merging.
 }
 
 WebAssemblyTargetMachine::~WebAssemblyTargetMachine() {}
@@ -184,6 +184,7 @@ void WebAssemblyPassConfig::addPostRegAlloc() {
   disablePass(&PrologEpilogCodeInserterID);
   // Fails with: should be run after register allocation.
   disablePass(&MachineCopyPropagationID);
+  disablePass(&TailDuplicateID);
 
   if (getOptLevel() != CodeGenOpt::None) {
     // Mark registers as representing wasm's expression stack.

test/CodeGen/WebAssembly/cfg-stackify.ll

@@ -459,9 +459,7 @@ exit:
 ; OPT-LABEL: test3:
 ; OPT: block
 ; OPT: br_if
-; OPT-NEXT: return
-; OPT-NEXT: .LBB{{[0-9]+}}_{{[0-9]+}}:
-; OPT-NEXT: end_block
+; OPT: .LBB{{[0-9]+}}_{{[0-9]+}}:
 ; OPT-NEXT: loop
 ; OPT-NEXT: block
 ; OPT-NEXT: block
@@ -513,44 +511,35 @@ if.end:
 ; CHECK:      block{{$}}
 ; CHECK-NEXT: block{{$}}
 ; CHECK:      br_if       0, $pop{{[0-9]+}}{{$}}
-; CHECK-NEXT: block{{$}}
-; CHECK:      br_if       0, $pop{{[0-9]+}}{{$}}
-; CHECK:      br_if       2, $pop{{[0-9]+}}{{$}}
+; CHECK:      br_if       1, $pop{{[0-9]+}}{{$}}
+; CHECK:      br          1{{$}}
 ; CHECK-NEXT: .LBB13_3:
 ; CHECK-NEXT: end_block{{$}}
-; CHECK-NEXT: return{{$}}
-; CHECK-NEXT: .LBB13_4:
-; CHECK-NEXT: end_block{{$}}
 ; CHECK-NEXT: block{{$}}
-; CHECK:      br_if       0, $pop{{[0-9]+}}{{$}}
-; CHECK:      br_if       1, $pop{{[0-9]+}}{{$}}
-; CHECK-NEXT: return{{$}}
-; CHECK-NEXT: .LBB13_7:
+; CHECK:      br_if 0, $pop{{[0-9]+}}{{$}}
+; CHECK:      br_if 1, $pop{{[0-9]+}}{{$}}
+; CHECK-NEXT: .LBB13_5:
 ; CHECK-NEXT: end_block{{$}}
 ; CHECK-NEXT: return{{$}}
-; CHECK-NEXT: .LBB13_8:
+; CHECK-NEXT: .LBB13_6:
 ; CHECK-NEXT: end_block{{$}}
 ; CHECK-NEXT: return{{$}}
 ; OPT-LABEL: test4:
 ; OPT-NEXT: .param       i32{{$}}
 ; OPT:      block{{$}}
 ; OPT-NEXT: block{{$}}
-; OPT-NEXT: block{{$}}
-; OPT:      br_if       0, $pop{{[0-9]+}}{{$}}
-; OPT-NEXT: block{{$}}
 ; OPT:      br_if       0, $pop{{[0-9]+}}{{$}}
-; OPT:      br_if       2, $pop{{[0-9]+}}{{$}}
+; OPT:      br_if       1, $pop{{[0-9]+}}{{$}}
+; OPT:      br          1{{$}}
 ; OPT-NEXT: .LBB13_3:
 ; OPT-NEXT: end_block{{$}}
-; OPT-NEXT: return{{$}}
-; OPT-NEXT: .LBB13_4:
-; OPT:      br_if       1, $pop{{[0-9]+}}{{$}}
+; OPT-NEXT: block{{$}}
 ; OPT:      br_if       0, $pop{{[0-9]+}}{{$}}
-; OPT-NEXT: return{{$}}
-; OPT-NEXT: .LBB13_7:
+; OPT:      br_if       1, $pop{{[0-9]+}}{{$}}
+; OPT-NEXT: .LBB13_5:
 ; OPT-NEXT: end_block{{$}}
 ; OPT-NEXT: return{{$}}
-; OPT-NEXT: .LBB13_8:
+; OPT-NEXT: .LBB13_6:
 ; OPT-NEXT: end_block{{$}}
 ; OPT-NEXT: return{{$}}
 define void @test4(i32 %t) {
@@ -826,13 +815,13 @@ bb3:
 ; CHECK-NOT:   block
 ; CHECK:       br_if     0, {{[^,]+}}{{$}}
 ; CHECK-NOT:   block
-; CHECK:       br_if     1, {{[^,]+}}{{$}}
-; CHECK-NEXT:  br        3{{$}}
+; CHECK:       br_if     3, {{[^,]+}}{{$}}
+; CHECK-NEXT:  br        1{{$}}
 ; CHECK-NEXT:  .LBB18_4:
 ; CHECK-NEXT:  end_block{{$}}
 ; CHECK-NOT:   block
-; CHECK:       br_if     0, {{[^,]+}}{{$}}
-; CHECK-NEXT:  br        2{{$}}
+; CHECK:       br_if     2, {{[^,]+}}{{$}}
+; CHECK-NEXT:  br        0{{$}}
 ; CHECK-NEXT:  .LBB18_5:
 ; CHECK-NOT:   block
 ; CHECK:       return{{$}}
@@ -1267,34 +1256,36 @@ bb50:
 ; CHECK:        block
 ; CHECK-NEXT:   block
 ; CHECK:        br_if       0, $pop{{.*}}{{$}}
-; CHECK-NEXT: .LBB24_1:
+; CHECK:        .LBB24_2:
 ; CHECK-NEXT:   block{{$}}
 ; CHECK-NEXT:   loop{{$}}
 ; CHECK:        br_if       1, $pop{{.*}}{{$}}
-; CHECK:        br_if       2, $pop{{.*}}{{$}}
-; CHECK-NEXT:   br          0{{$}}
-; CHECK-NEXT:   .LBB24_3:
+; CHECK:        br_if       0, ${{.*}}{{$}}
+; CHECK-NEXT:   br          2{{$}}
+; CHECK-NEXT:   .LBB24_4:
 ; CHECK-NEXT:   end_loop{{$}}
-; CHECK:        .LBB24_4:
+; CHECK:        .LBB24_5:
 ; CHECK-NEXT:   end_block{{$}}
 ; CHECK:        br_if       1, $pop{{.*}}{{$}}
 ; CHECK:        return{{$}}
-; CHECK:        .LBB24_6:
-; CHECK-NEXT:   end_block{{$}}
-; CHECK:        return{{$}}
 ; CHECK:        .LBB24_7:
 ; CHECK-NEXT:   end_block{{$}}
+; CHECK:        .LBB24_8:
+; CHECK-NEXT:   end_block{{$}}
 ; CHECK-NEXT:   return{{$}}
 ; OPT-LABEL: test15:
 ; OPT:        block
+; OPT:        block
 ; OPT-NEXT:   i32.const   $push
 ; OPT-NEXT:   i32.const   $push
 ; OPT-NEXT:   i32.eq      $push{{.*}}=, $pop{{.*}}, $pop{{.*}}{{$}}
 ; OPT-NEXT:   br_if       0, $pop{{.*}}{{$}}
 ; OPT-NEXT:   call        test15_callee1@FUNCTION{{$}}
-; OPT-NEXT:   return{{$}}
+; OPT-NEXT:   br          1{{$}}
 ; OPT-NEXT: .LBB24_2:
 ; OPT-NEXT:   end_block
+; OPT-NEXT:   i32.const
+; OPT-NEXT: .LBB24_3:
 ; OPT-NEXT:   block
 ; OPT-NEXT:   loop
 %0 = type { i8, i32 }