[llvm] a320f87 - [WebAssembly] Fix debug locations for ExplicitLocals pass

[Wouter van Oortmerssen via llvm-commits]

Author: Wouter van Oortmerssen
Date: 2021-11-04T11:38:03-07:00
New Revision: a320f877cec6f11e275b44ac3a239931e00b8cc8

URL: https://github.com/llvm/llvm-project/commit/a320f877cec6f11e275b44ac3a239931e00b8cc8
DIFF: https://github.com/llvm/llvm-project/commit/a320f877cec6f11e275b44ac3a239931e00b8cc8.diff

LOG: [WebAssembly] Fix debug locations for ExplicitLocals pass

This is a reworked version of the reverted patch: https://reviews.llvm.org/D112487
Note that
a) it doesn't need the test changes anymore, and
b) I checked at least locally it passes other.test_pthread_lsan_leak

Differential Revision: https://reviews.llvm.org/D113208

Added: 
    

Modified: 
    llvm/lib/Target/WebAssembly/WebAssemblyExplicitLocals.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Target/WebAssembly/WebAssemblyExplicitLocals.cpp b/llvm/lib/Target/WebAssembly/WebAssemblyExplicitLocals.cpp
index a933d1a4f421..910a4e5e0d1a 100644
--- a/llvm/lib/Target/WebAssembly/WebAssemblyExplicitLocals.cpp
+++ b/llvm/lib/Target/WebAssembly/WebAssemblyExplicitLocals.cpp
@@ -379,9 +379,14 @@ bool WebAssemblyExplicitLocals::runOnMachineFunction(MachineFunction &MF) {
         const TargetRegisterClass *RC = MRI.getRegClass(OldReg);
         Register NewReg = MRI.createVirtualRegister(RC);
         unsigned Opc = getLocalGetOpcode(RC);
-        InsertPt =
-            BuildMI(MBB, InsertPt, MI.getDebugLoc(), TII->get(Opc), NewReg)
-                .addImm(LocalId);
+        // Use a InsertPt as our DebugLoc, since MI may be discontinuous from
+        // the where this local is being inserted, causing non-linear stepping
+        // in the debugger or function entry points where variables aren't live
+        // yet. Alternative is previous instruction, but that is strictly worse
+        // since it can point at the previous statement.
+        // See crbug.com/1251909, crbug.com/1249745
+        InsertPt = BuildMI(MBB, InsertPt, InsertPt->getDebugLoc(),
+                           TII->get(Opc), NewReg).addImm(LocalId);
         MO.setReg(NewReg);
         MFI.stackifyVReg(MRI, NewReg);
         Changed = true;