Refactor code used in InstCombine::FoldAndOfICmps to new file.

This will be used by SimplifyCfg in a later commit.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@146803 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 97 insertions, 0 deletions

diff --git a/lib/Transforms/Utils/CmpInstAnalysis.cpp b/lib/Transforms/Utils/CmpInstAnalysis.cpp
new file mode 100644
index 0000000000..e336e9a5a2
--- /dev/null
+++ b/lib/Transforms/Utils/CmpInstAnalysis.cpp
@@ -0,0 +1,97 @@
+//===- CmpInstAnalysis.cpp - Utils to help fold compares ---------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// This file holds routines to help analyse compare instructions
+// and fold them into constants or other compare instructions
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Transforms/Utils/CmpInstAnalysis.h"
+#include "llvm/Constants.h"
+#include "llvm/Instructions.h"
+
+using namespace llvm;
+
+/// getICmpCode - Encode a icmp predicate into a three bit mask.  These bits
+/// are carefully arranged to allow folding of expressions such as:
+///
+///      (A < B) | (A > B) --> (A != B)
+///
+/// Note that this is only valid if the first and second predicates have the
+/// same sign. Is illegal to do: (A u< B) | (A s> B)
+///
+/// Three bits are used to represent the condition, as follows:
+///   0  A > B
+///   1  A == B
+///   2  A < B
+///
+/// <=>  Value  Definition
+/// 000     0   Always false
+/// 001     1   A >  B
+/// 010     2   A == B
+/// 011     3   A >= B
+/// 100     4   A <  B
+/// 101     5   A != B
+/// 110     6   A <= B
+/// 111     7   Always true
+///
+unsigned llvm::getICmpCode(const ICmpInst *ICI, bool InvertPred) {
+  ICmpInst::Predicate Pred = InvertPred ? ICI->getInversePredicate()
+                                        : ICI->getPredicate();
+  switch (Pred) {
+      // False -> 0
+    case ICmpInst::ICMP_UGT: return 1;  // 001
+    case ICmpInst::ICMP_SGT: return 1;  // 001
+    case ICmpInst::ICMP_EQ:  return 2;  // 010
+    case ICmpInst::ICMP_UGE: return 3;  // 011
+    case ICmpInst::ICMP_SGE: return 3;  // 011
+    case ICmpInst::ICMP_ULT: return 4;  // 100
+    case ICmpInst::ICMP_SLT: return 4;  // 100
+    case ICmpInst::ICMP_NE:  return 5;  // 101
+    case ICmpInst::ICMP_ULE: return 6;  // 110
+    case ICmpInst::ICMP_SLE: return 6;  // 110
+      // True -> 7
+    default:
+      llvm_unreachable("Invalid ICmp predicate!");
+      return 0;
+  }
+}
+
+/// getICmpValue - This is the complement of getICmpCode, which turns an
+/// opcode and two operands into either a constant true or false, or the
+/// predicate for a new ICmp instruction. The sign is passed in to determine
+/// which kind of predicate to use in the new icmp instruction.
+/// Non-NULL return value will be a true or false constant.
+/// NULL return means a new ICmp is needed.  The predicate for which is
+/// output in NewICmpPred.
+Value *llvm::getICmpValue(bool Sign, unsigned Code, Value *LHS, Value *RHS,
+                          CmpInst::Predicate &NewICmpPred) {
+  switch (Code) {
+    default: assert(0 && "Illegal ICmp code!");
+    case 0: // False.
+      return ConstantInt::get(CmpInst::makeCmpResultType(LHS->getType()), 0);
+    case 1: NewICmpPred = Sign ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT; break;
+    case 2: NewICmpPred = ICmpInst::ICMP_EQ; break;
+    case 3: NewICmpPred = Sign ? ICmpInst::ICMP_SGE : ICmpInst::ICMP_UGE; break;
+    case 4: NewICmpPred = Sign ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT; break;
+    case 5: NewICmpPred = ICmpInst::ICMP_NE; break;
+    case 6: NewICmpPred = Sign ? ICmpInst::ICMP_SLE : ICmpInst::ICMP_ULE; break;
+    case 7: // True.
+      return ConstantInt::get(CmpInst::makeCmpResultType(LHS->getType()), 1);
+  }
+  return NULL;
+}
+
+/// PredicatesFoldable - Return true if both predicates match sign or if at
+/// least one of them is an equality comparison (which is signless).
+bool llvm::PredicatesFoldable(ICmpInst::Predicate p1, ICmpInst::Predicate p2) {
+  return (CmpInst::isSigned(p1) == CmpInst::isSigned(p2)) ||
+         (CmpInst::isSigned(p1) && ICmpInst::isEquality(p2)) ||
+         (CmpInst::isSigned(p2) && ICmpInst::isEquality(p1));
+}