[PATCH] D42119: [CodeGen] Skip some instructions that shouldn't affect shrink-wrapping

[Francis Visoiu Mistrih via Phabricator via llvm-commits]

thegameg created this revision.
thegameg added reviewers: MatzeB, qcolombet, aprantl.

r320606 <https://reviews.llvm.org/rL320606> checked for `MI.isMetaInstruction` which skips all DBG_VALUEs.

This also skips `IMPLICIT_DEFs` and other instructions that may def / read a register.


https://reviews.llvm.org/D42119

Files:
  lib/CodeGen/ShrinkWrap.cpp


Index: lib/CodeGen/ShrinkWrap.cpp
===================================================================
--- lib/CodeGen/ShrinkWrap.cpp
+++ lib/CodeGen/ShrinkWrap.cpp
@@ -240,18 +240,17 @@
 
 bool ShrinkWrap::useOrDefCSROrFI(const MachineInstr &MI,
                                  RegScavenger *RS) const {
-  // Ignore DBG_VALUE and other meta instructions that must not affect codegen.
-  if (MI.isMetaInstruction())
-    return false;
-
   if (MI.getOpcode() == FrameSetupOpcode ||
       MI.getOpcode() == FrameDestroyOpcode) {
     DEBUG(dbgs() << "Frame instruction: " << MI << '\n');
     return true;
   }
   for (const MachineOperand &MO : MI.operands()) {
     bool UseOrDefCSR = false;
     if (MO.isReg()) {
+      // Ignore instructions like DBG_VALUE which don't read/def the register.
+      if (!MO.isDef() && !MO.readsReg())
+        continue;
       unsigned PhysReg = MO.getReg();
       if (!PhysReg)
         continue;
@@ -267,7 +266,8 @@
         }
       }
     }
-    if (UseOrDefCSR || MO.isFI()) {
+    // Skip FrameIndex operands in DBG_VALUE instructions.
+    if (UseOrDefCSR || (MO.isFI() && !MI.isDebugValue())) {
       DEBUG(dbgs() << "Use or define CSR(" << UseOrDefCSR << ") or FI("
                    << MO.isFI() << "): " << MI << '\n');
       return true;


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