[llvm] r258694 - [WebAssembly] Fix unbalanced register stack code in the case of late DCE.

[Dan Gohman via llvm-commits]

Author: djg
Date: Mon Jan 25 10:48:44 2016
New Revision: 258694

URL: http://llvm.org/viewvc/llvm-project?rev=258694&view=rev
Log:
[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.

Modified:
    llvm/trunk/lib/Target/WebAssembly/WebAssemblyRegNumbering.cpp
    llvm/trunk/test/CodeGen/WebAssembly/cfg-stackify.ll

Modified: llvm/trunk/lib/Target/WebAssembly/WebAssemblyRegNumbering.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/WebAssembly/WebAssemblyRegNumbering.cpp?rev=258694&r1=258693&r2=258694&view=diff
==============================================================================
--- llvm/trunk/lib/Target/WebAssembly/WebAssemblyRegNumbering.cpp (original)
+++ llvm/trunk/lib/Target/WebAssembly/WebAssemblyRegNumbering.cpp Mon Jan 25 10:48:44 2016
@@ -92,6 +92,9 @@ bool WebAssemblyRegNumbering::runOnMachi
   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::runOnMachi
       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++);

Modified: llvm/trunk/test/CodeGen/WebAssembly/cfg-stackify.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/WebAssembly/cfg-stackify.ll?rev=258694&r1=258693&r2=258694&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/WebAssembly/cfg-stackify.ll (original)
+++ llvm/trunk/test/CodeGen/WebAssembly/cfg-stackify.ll Mon Jan 25 10:48:44 2016
@@ -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() {