[PATCH] D78087: [MachineSink] Fix for breaking phi edges with instructions with multiple defs

[Dave Green via Phabricator via llvm-commits]

dmgreen created this revision.
dmgreen added reviewers: fhahn, SjoerdMeijer, efriedma.
Herald added a subscriber: hiraditya.

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.


https://reviews.llvm.org/D78087

Files:
  llvm/lib/CodeGen/MachineSink.cpp
  llvm/test/CodeGen/ARM/machine-sink-multidef.ll


Index: llvm/test/CodeGen/ARM/machine-sink-multidef.ll
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/ARM/machine-sink-multidef.ll
@@ -0,0 +1,56 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc < %s -mtriple=arm-none-eabi | FileCheck %s
+
+%struct.anon.1.19.23.27.35.49.55.57.59.61.89.95 = type { i32, i32 }
+
+ at e = external dso_local unnamed_addr constant [2 x %struct.anon.1.19.23.27.35.49.55.57.59.61.89.95], align 4
+ at f = external dso_local local_unnamed_addr global i32, align 4
+
+define arm_aapcscc void @g() {
+; CHECK-LABEL: g:
+; CHECK:       @ %bb.0: @ %entry
+; CHECK-NEXT:    .save {r11, lr}
+; CHECK-NEXT:    push {r11, lr}
+; CHECK-NEXT:    ldr r0, .LCPI0_0
+; CHECK-NEXT:    mov r2, #0
+; CHECK-NEXT:    ldr r1, .LCPI0_1
+; CHECK-NEXT:    cmp r2, #0
+; CHECK-NEXT:    ldr r0, [r0]
+; CHECK-NEXT:    ldr r0, [r1, r0, lsl #3]!
+; CHECK-NEXT:    moveq r0, #0
+; CHECK-NEXT:    cmp r2, #0
+; CHECK-NEXT:    popne {r11, lr}
+; CHECK-NEXT:    movne pc, lr
+; CHECK-NEXT:    ldr r1, [r1, #4]
+; CHECK-NEXT:    bl k
+; CHECK-NEXT:    .p2align 2
+; CHECK-NEXT:  @ %bb.1:
+; CHECK-NEXT:  .LCPI0_0:
+; CHECK-NEXT:    .long f
+; CHECK-NEXT:  .LCPI0_1:
+; CHECK-NEXT:    .long e
+entry:
+  %0 = load i32, i32* @f, align 4
+  %c = getelementptr inbounds [2 x %struct.anon.1.19.23.27.35.49.55.57.59.61.89.95], [2 x %struct.anon.1.19.23.27.35.49.55.57.59.61.89.95]* @e, i32 0, i32 %0, i32 0
+  %1 = load i32, i32* %c, align 4
+  %d = getelementptr inbounds [2 x %struct.anon.1.19.23.27.35.49.55.57.59.61.89.95], [2 x %struct.anon.1.19.23.27.35.49.55.57.59.61.89.95]* @e, i32 0, i32 %0, i32 1
+  %2 = load i32, i32* %d, align 4
+  br i1 undef, label %land.lhs.true, label %if.end
+
+land.lhs.true:                                    ; preds = %entry
+  br label %if.end
+
+if.end:                                           ; preds = %land.lhs.true, %entry
+  %h.0 = phi i32 [ %1, %entry ], [ 0, %land.lhs.true ]
+  br i1 undef, label %if.end7, label %if.then5
+
+if.then5:                                         ; preds = %if.end
+  %call6 = call arm_aapcscc i32 bitcast (i32 (...)* @k to i32 (i32, i32)*)(i32 %h.0, i32 %2)
+  unreachable
+
+if.end7:                                          ; preds = %if.end
+  ret void
+}
+
+declare dso_local arm_aapcscc i32 @k(...)
+
Index: llvm/lib/CodeGen/MachineSink.cpp
===================================================================
--- llvm/lib/CodeGen/MachineSink.cpp
+++ llvm/lib/CodeGen/MachineSink.cpp
@@ -280,19 +280,21 @@
   // %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;
+  bool LocalBreakPHIEdge = true;
   for (MachineOperand &MO : MRI->use_nodbg_operands(Reg)) {
     MachineInstr *UseInst = MO.getParent();
-    unsigned OpNo = &MO - &UseInst->getOperand(0);
+    unsigned OpNo = UseInst->getOperandNo(&MO);
     MachineBasicBlock *UseBlock = UseInst->getParent();
     if (!(UseBlock == MBB && UseInst->isPHI() &&
           UseInst->getOperand(OpNo+1).getMBB() == DefMBB)) {
-      BreakPHIEdge = false;
+      LocalBreakPHIEdge = false;
       break;
     }
   }
-  if (BreakPHIEdge)
+  if (LocalBreakPHIEdge) {
+    BreakPHIEdge = true;
     return true;
+  }
 
   for (MachineOperand &MO : MRI->use_nodbg_operands(Reg)) {
     // Determine the block of the use.


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