Add PredicateInfo utility and printing pass

Summary:
This patch adds a utility to build extended SSA (see "ABCD: eliminating
array bounds checks on demand"), and an intrinsic to support it. This
is then used to get functionality equivalent to propagateEquality in
GVN, in NewGVN (without having to replace instructions as we go). It
would work similarly in SCCP or other passes. This has been talked
about a few times, so i built a real implementation and tried to
productionize it.

Copies are inserted for operands used in assumes and conditional
branches that are based on comparisons (see below for more)

Every use affected by the predicate is renamed to the appropriate
intrinsic result.

E.g.
%cmp = icmp eq i32 %x, 50
br i1 %cmp, label %true, label %false
true:
ret i32 %x
false:
ret i32 1

will become

%cmp = icmp eq i32, %x, 50
br i1 %cmp, label %true, label %false
true:
; Has predicate info
; branch predicate info { TrueEdge: 1 Comparison: %cmp = icmp eq i32 %x, 50 }
%x.0 = call @llvm.ssa_copy.i32(i32 %x)
ret i32 %x.0
false:
ret i23 1

(you can use -print-predicateinfo to get an annotated-with-predicateinfo dump)

This enables us to easily determine what operations are affected by a
given predicate, and how operations affected by a chain of
predicates.

Reviewers: davide, sanjoy

Subscribers: mgorny, llvm-commits, Prazek

Differential Revision: https://reviews.llvm.org/D29519

Update for review comments

Fix a bug Nuno noticed where we are giving information about and/or on edges where the info is not useful and easy to use wrong

Update for review comments

llvm-svn: 294351

1 files changed, 1 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/Utils/Utils.cpp b/llvm/lib/Transforms/Utils/Utils.cpp
index 7b9de2eadc6..dd47c5532c5 100644
--- a/llvm/lib/Transforms/Utils/Utils.cpp
+++ b/llvm/lib/Transforms/Utils/Utils.cpp
@@ -38,6 +38,7 @@ void llvm::initializeTransformUtils(PassRegistry &Registry) {
   initializeMemorySSAWrapperPassPass(Registry);
   initializeMemorySSAPrinterLegacyPassPass(Registry);
   initializeStripGCRelocatesPass(Registry);
+  initializePredicateInfoPrinterLegacyPassPass(Registry);
 }
 
 /// LLVMInitializeTransformUtils - C binding for initializeTransformUtilsPasses.