[WebAssembly] Fix unbalanced register stack code in the case of late DCE.

Instructions can be DCE'd after the RegStackify pass. If the instruction which
would be the pop for what would be a push is removed, don't use a push.

llvm-svn: 258694

diff --git a/llvm/lib/Target/WebAssembly/WebAssemblyRegNumbering.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyRegNumbering.cpp
index 88c50a0..a76cb81 100644 (file)
--- a/llvm/lib/Target/WebAssembly/WebAssemblyRegNumbering.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyRegNumbering.cpp
@@ -92,6 +92,9 @@ bool WebAssemblyRegNumbering::runOnMachineFunction(MachineFunction &MF) {
   unsigned CurReg = MFI.getParams().size();
   for (unsigned VRegIdx = 0; VRegIdx < NumVRegs; ++VRegIdx) {
     unsigned VReg = TargetRegisterInfo::index2VirtReg(VRegIdx);
+    // Skip unused registers.
+    if (MRI.use_empty(VReg))
+      continue;
     // Handle stackified registers.
     if (MFI.isVRegStackified(VReg)) {
       DEBUG(dbgs() << "VReg " << VReg << " -> WAReg "
@@ -99,9 +102,6 @@ bool WebAssemblyRegNumbering::runOnMachineFunction(MachineFunction &MF) {
       MFI.setWAReg(VReg, INT32_MIN | NumStackRegs++);
       continue;
     }
-    // Skip unused registers.
-    if (MRI.use_empty(VReg))
-      continue;
     if (MFI.getWAReg(VReg) == WebAssemblyFunctionInfo::UnusedReg) {
       DEBUG(dbgs() << "VReg " << VReg << " -> WAReg " << CurReg << "\n");
       MFI.setWAReg(VReg, CurReg++);

diff --git a/llvm/test/CodeGen/WebAssembly/cfg-stackify.ll b/llvm/test/CodeGen/WebAssembly/cfg-stackify.ll
index f5b4b77..a1ff4ee 100644 (file)
--- a/llvm/test/CodeGen/WebAssembly/cfg-stackify.ll
+++ b/llvm/test/CodeGen/WebAssembly/cfg-stackify.ll
@@ -1176,9 +1176,9 @@ bb5:
 ; CHECK-NEXT: .LBB23_2:{{$}}
 ; CHECK-NEXT:     end_loop{{$}}
 ; CHECK-NEXT:     loop{{$}}
+; CHECK-NEXT:     i32.const   $discard=, 0{{$}}
 ; CHECK-NEXT:     i32.const   $push1=, 0{{$}}
-; CHECK-NEXT:     i32.const   $push2=, 0{{$}}
-; CHECK-NEXT:     br_if       $pop2, 0{{$}}
+; CHECK-NEXT:     br_if       $pop1, 0{{$}}
 ; CHECK-NEXT:     end_loop{{$}}
 ; CHECK-NEXT:     return{{$}}
 define void @test14() {