[VPlan] Add printPhiOperands to VPPhiAccessors, use for wide phis.

(NFC modulo debug output changes)

Add generic helper to print phi operands (incoming values) together with
their incoming blocks.

As more and more transforms are added, keeping the incoming blocks of
phis becomes more important. Print incoming blocks via VPPhiAcessors, to
make debugging easier.

Author: fhahn

llvm/lib/Transforms/Vectorize/VPlan.h

@@ -1201,6 +1201,11 @@ class VPPhiAccessors {
 
   /// Returns the number of incoming values, also number of incoming blocks.
   unsigned getNumIncoming() const { return getAsRecipe()->getNumOperands(); }
+
+#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
+  /// Print the recipe.
+  void printPhiOperands(raw_ostream &O, VPSlotTracker &SlotTracker) const;
+#endif
 };
 
 /// An overlay for VPIRInstructions wrapping PHI nodes enabling convenient use

llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp

@@ -1197,6 +1197,20 @@ void VPIRPhi::execute(VPTransformState &State) {
   State.Builder.SetInsertPoint(Phi->getParent(), std::next(Phi->getIterator()));
 }
 
+#if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
+void VPPhiAccessors::printPhiOperands(raw_ostream &O,
+                                      VPSlotTracker &SlotTracker) const {
+  interleaveComma(enumerate(getAsRecipe()->operands()), O,
+                  [this, &O, &SlotTracker](auto Op) {
+                    O << "[ ";
+                    Op.value()->printAsOperand(O, SlotTracker);
+                    O << ", ";
+                    getIncomingBlock(Op.index())->printAsOperand(O);
+                    O << " ]";
+                  });
+}
+#endif
+
 #if !defined(NDEBUG) || defined(LLVM_ENABLE_DUMP)
 void VPIRPhi::print(raw_ostream &O, const Twine &Indent,
                     VPSlotTracker &SlotTracker) const {
@@ -3809,7 +3823,7 @@ void VPWidenPHIRecipe::print(raw_ostream &O, const Twine &Indent,
 
   printAsOperand(O, SlotTracker);
   O << " = phi ";
-  printOperands(O, SlotTracker);
+  printPhiOperands(O, SlotTracker);
 }
 #endif
 

llvm/test/Transforms/LoopVectorize/vplan-printing-outer-loop.ll

@@ -13,14 +13,14 @@ define void @foo(i64 %n) {
 ; CHECK-NEXT: Successor(s): outer.header
 ; CHECK-EMPTY:
 ; CHECK-NEXT: outer.header:
-; CHECK-NEXT:   WIDEN-PHI ir<%outer.iv> = phi ir<%outer.iv.next>, ir<0>
+; CHECK-NEXT:   WIDEN-PHI ir<%outer.iv> = phi [ ir<%outer.iv.next>, outer.latch ], [ ir<0>, ir-bb<entry> ]
 ; CHECK-NEXT:   EMIT ir<%gep.1> = getelementptr ir<@arr2>, ir<0>, ir<%outer.iv>
 ; CHECK-NEXT:   EMIT store ir<%outer.iv>, ir<%gep.1>
 ; CHECK-NEXT:   EMIT ir<%add> = add ir<%outer.iv>, ir<%n>
 ; CHECK-NEXT: Successor(s): inner
 ; CHECK-EMPTY:
 ; CHECK-NEXT: inner:
-; CHECK-NEXT:   WIDEN-PHI ir<%inner.iv> = phi ir<%inner.iv.next>, ir<0>
+; CHECK-NEXT:   WIDEN-PHI ir<%inner.iv> = phi [ ir<%inner.iv.next>, inner ], [ ir<0>, outer.header ]
 ; CHECK-NEXT:   EMIT ir<%gep.2> = getelementptr ir<@arr>, ir<0>, ir<%inner.iv>, ir<%outer.iv>
 ; CHECK-NEXT:   EMIT store ir<%add>, ir<%gep.2>
 ; CHECK-NEXT:   EMIT ir<%inner.iv.next> = add ir<%inner.iv>, ir<1>

llvm/unittests/Transforms/Vectorize/VPlanHCFGTest.cpp

@@ -122,7 +122,7 @@ compound=true
     N2 [label =
       "vector.body:\l" +
       "  EMIT vp\<%2\> = CANONICAL-INDUCTION ir\<0\>, vp\<%index.next\>\l" +
-      "  WIDEN-PHI ir\<%indvars.iv\> = phi ir\<0\>, ir\<%indvars.iv.next\>\l" +
+      "  WIDEN-PHI ir\<%indvars.iv\> = phi [ ir\<0\>, vector.ph ], [ ir\<%indvars.iv.next\>, vector.body ]\l" +
       "  EMIT ir\<%arr.idx\> = getelementptr ir\<%A\>, ir\<%indvars.iv\>\l" +
       "  EMIT ir\<%l1\> = load ir\<%arr.idx\>\l" +
       "  EMIT ir\<%res\> = add ir\<%l1\>, ir\<10\>\l" +
@@ -291,7 +291,7 @@ compound=true
     N2 [label =
       "vector.body:\l" +
       "  EMIT vp\<%2\> = CANONICAL-INDUCTION ir\<0\>, vp\<%index.next\>\l" +
-      "  WIDEN-PHI ir\<%iv\> = phi ir\<0\>, ir\<%iv.next\>\l" +
+      "  WIDEN-PHI ir\<%iv\> = phi [ ir\<0\>, vector.ph ], [ ir\<%iv.next\>, loop.latch ]\l" +
       "  EMIT ir\<%arr.idx\> = getelementptr ir\<%A\>, ir\<%iv\>\l" +
       "  EMIT ir\<%l1\> = load ir\<%arr.idx\>\l" +
       "  EMIT ir\<%c\> = icmp ir\<%l1\>, ir\<0\>\l" +