[llvm] [PredicateInfo] Support existing `PredicateType` by adding `PredicatePHI` when needing introduction of phi nodes (PR #151132)

[Nikita Popov via llvm-commits]

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@@ -0,0 +1,43 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S -passes=print-predicateinfo < %s 2>&1 >/dev/null | FileCheck %s
+
+ at p = local_unnamed_addr global i32 0
+
+define noundef i32 @h5diff(i32 %0, i1 %1) local_unnamed_addr #0 {
+; CHECK-LABEL: @h5diff(
+; CHECK-NEXT:    [[COND:%.*]] = icmp eq i32 [[TMP0:%.*]], 0
+; CHECK-NEXT:    br i1 [[TMP1:%.*]], label [[TMP3:%.*]], label [[TMP4:%.*]]
+; CHECK:       3:
+; CHECK-NEXT:    store i32 1, ptr @p, align 4
+; CHECK:         [[DOT0:%.*]] = call i32 @llvm.ssa.copy.i32(i32 [[TMP0]])
+; CHECK-NEXT:    br i1 [[COND]], label [[TMP5:%.*]], label [[COMMON_RET:%.*]]
+; CHECK:       common.ret:
+; CHECK-NEXT:    ret i32 0
+; CHECK:       4:
+; CHECK-NEXT:    store i32 2, ptr @p, align 4
+; CHECK:         [[DOT1:%.*]] = call i32 @llvm.ssa.copy.i32(i32 [[TMP0]])
+; CHECK-NEXT:    br i1 [[COND]], label [[TMP5]], label [[COMMON_RET]]
+; CHECK:       5:
+; CHECK-NEXT:    [[DOTPREDICATE_PHI:%.*]] = phi i32 [ [[DOT1]], [[TMP4]] ], [ [[DOT0]], [[TMP3]] ]
+; CHECK:         [[TMP6:%.*]] = call i32 @llvm.ssa.copy.i32(i32 [[TMP0]])
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nikic wrote:

Sorry, I still do not understand the purpose of the PredicatePHIs. How does it make things "more sophisticated and maintainable"?

https://github.com/llvm/llvm-project/pull/151132