[MachineSink] Fix for breaking phi edges with instructions with multiple defs

BreakPHIEdge would be set based on whether the instruction needs to
insert a new critical edge to allow sinking into a block where the uses
are PHI nodes. But for instructions with multiple defs it would be reset
on the second def, allowing the instruciton to sink where it should not.

Fixes PR44981

Differential Revision: https://reviews.llvm.org/D78087

1 files changed, 13 insertions, 17 deletions

diff --git a/llvm/lib/CodeGen/MachineSink.cpp b/llvm/lib/CodeGen/MachineSink.cpp
index ac342ba..01a7be4 100644
--- a/llvm/lib/CodeGen/MachineSink.cpp
+++ b/llvm/lib/CodeGen/MachineSink.cpp
@@ -269,30 +269,26 @@ MachineSinking::AllUsesDominatedByBlock(unsigned Reg,
   // into and they are all PHI nodes. In this case, machine-sink must break
   // the critical edge first. e.g.
   //
-  // %bb.1: derived from LLVM BB %bb4.preheader
+  // %bb.1:
   //   Predecessors according to CFG: %bb.0
   //     ...
-  //     %reg16385 = DEC64_32r %reg16437, implicit-def dead %eflags
+  //     %def = DEC64_32r %x, implicit-def dead %eflags
   //     ...
   //     JE_4 <%bb.37>, implicit %eflags
   //   Successors according to CFG: %bb.37 %bb.2
   //
-  // %bb.2: derived from LLVM BB %bb.nph
-  //   Predecessors according to CFG: %bb.0 %bb.1
-  //     %reg16386 = PHI %reg16434, %bb.0, %reg16385, %bb.1
-  BreakPHIEdge = true;
-  for (MachineOperand &MO : MRI->use_nodbg_operands(Reg)) {
-    MachineInstr *UseInst = MO.getParent();
-    unsigned OpNo = &MO - &UseInst->getOperand(0);
-    MachineBasicBlock *UseBlock = UseInst->getParent();
-    if (!(UseBlock == MBB && UseInst->isPHI() &&
-          UseInst->getOperand(OpNo+1).getMBB() == DefMBB)) {
-      BreakPHIEdge = false;
-      break;
-    }
-  }
-  if (BreakPHIEdge)
+  // %bb.2:
+  //     %p = PHI %y, %bb.0, %def, %bb.1
+  if (llvm::all_of(MRI->use_nodbg_operands(Reg), [&](MachineOperand &MO) {
+        MachineInstr *UseInst = MO.getParent();
+        unsigned OpNo = UseInst->getOperandNo(&MO);
+        MachineBasicBlock *UseBlock = UseInst->getParent();
+        return UseBlock == MBB && UseInst->isPHI() &&
+               UseInst->getOperand(OpNo + 1).getMBB() == DefMBB;
+      })) {
+    BreakPHIEdge = true;
     return true;
+  }
 
   for (MachineOperand &MO : MRI->use_nodbg_operands(Reg)) {
     // Determine the block of the use.