From 599e65b1ff51d4f92ebf68696adb0955788db051 Mon Sep 17 00:00:00 2001
From: Sanjay Patel <spatel@rotateright.com>
Date: Sun, 7 May 2017 15:11:40 +0000
Subject: [InstSimplify] use ConstantRange to simplify or-of-icmps

We can simplify (or (icmp X, C1), (icmp X, C2)) to 'true' or one of the icmps in many cases.
I had to check some of these with Alive to prove to myself it's right, but everything seems
to check out. Eg, the deleted code in instcombine was completely ignoring predicates with
mismatched signedness.

This is a follow-up to:
https://reviews.llvm.org/rL301260
https://reviews.llvm.org/D32143

llvm-svn: 302370
---
 .../Transforms/InstCombine/InstCombineAndOrXor.cpp | 57 +---------------------
 1 file changed, 2 insertions(+), 55 deletions(-)

(limited to 'llvm/lib/Transforms/InstCombine')

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
index c7092bf3a39..b114801cc1c 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -1834,25 +1834,8 @@ Value *InstCombiner::FoldOrOfICmps(ICmpInst *LHS, ICmpInst *RHS,
     case ICmpInst::ICMP_UGT: // (X == 13 | X u> 14) -> no change
     case ICmpInst::ICMP_SGT: // (X == 13 | X s> 14) -> no change
       break;
-    case ICmpInst::ICMP_NE:  // (X == 13 | X != 15) -> X != 15
-    case ICmpInst::ICMP_ULT: // (X == 13 | X u< 15) -> X u< 15
-    case ICmpInst::ICMP_SLT: // (X == 13 | X s< 15) -> X s< 15
-      return RHS;
     }
     break;
-  case ICmpInst::ICMP_NE:
-    switch (PredR) {
-    default:
-      llvm_unreachable("Unknown integer condition code!");
-    case ICmpInst::ICMP_EQ:  // (X != 13 | X == 15) -> X != 13
-    case ICmpInst::ICMP_UGT: // (X != 13 | X u> 15) -> X != 13
-    case ICmpInst::ICMP_SGT: // (X != 13 | X s> 15) -> X != 13
-      return LHS;
-    case ICmpInst::ICMP_NE:  // (X != 13 | X != 15) -> true
-    case ICmpInst::ICMP_ULT: // (X != 13 | X u< 15) -> true
-    case ICmpInst::ICMP_SLT: // (X != 13 | X s< 15) -> true
-      return Builder->getTrue();
-    }
   case ICmpInst::ICMP_ULT:
     switch (PredR) {
     default:
@@ -1860,15 +1843,9 @@ Value *InstCombiner::FoldOrOfICmps(ICmpInst *LHS, ICmpInst *RHS,
     case ICmpInst::ICMP_EQ: // (X u< 13 | X == 14) -> no change
       break;
     case ICmpInst::ICMP_UGT: // (X u< 13 | X u> 15) -> (X-13) u> 2
-      // If RHSC is [us]MAXINT, it is always false.  Not handling
-      // this can cause overflow.
-      if (RHSC->isMaxValue(false))
-        return LHS;
+      assert(!RHSC->isMaxValue(false) && "Missed icmp simplification");
       return insertRangeTest(LHS0, LHSC->getValue(), RHSC->getValue() + 1,
                              false, false);
-    case ICmpInst::ICMP_NE:  // (X u< 13 | X != 15) -> X != 15
-    case ICmpInst::ICMP_ULT: // (X u< 13 | X u< 15) -> X u< 15
-      return RHS;
     }
     break;
   case ICmpInst::ICMP_SLT:
@@ -1878,39 +1855,9 @@ Value *InstCombiner::FoldOrOfICmps(ICmpInst *LHS, ICmpInst *RHS,
     case ICmpInst::ICMP_EQ: // (X s< 13 | X == 14) -> no change
       break;
     case ICmpInst::ICMP_SGT: // (X s< 13 | X s> 15) -> (X-13) s> 2
-      // If RHSC is [us]MAXINT, it is always false.  Not handling
-      // this can cause overflow.
-      if (RHSC->isMaxValue(true))
-        return LHS;
+      assert(!RHSC->isMaxValue(true) && "Missed icmp simplification");
       return insertRangeTest(LHS0, LHSC->getValue(), RHSC->getValue() + 1, true,
                              false);
-    case ICmpInst::ICMP_NE:  // (X s< 13 | X != 15) -> X != 15
-    case ICmpInst::ICMP_SLT: // (X s< 13 | X s< 15) -> X s< 15
-      return RHS;
-    }
-    break;
-  case ICmpInst::ICMP_UGT:
-    switch (PredR) {
-    default:
-      llvm_unreachable("Unknown integer condition code!");
-    case ICmpInst::ICMP_EQ:  // (X u> 13 | X == 15) -> X u> 13
-    case ICmpInst::ICMP_UGT: // (X u> 13 | X u> 15) -> X u> 13
-      return LHS;
-    case ICmpInst::ICMP_NE:  // (X u> 13 | X != 15) -> true
-    case ICmpInst::ICMP_ULT: // (X u> 13 | X u< 15) -> true
-      return Builder->getTrue();
-    }
-    break;
-  case ICmpInst::ICMP_SGT:
-    switch (PredR) {
-    default:
-      llvm_unreachable("Unknown integer condition code!");
-    case ICmpInst::ICMP_EQ:  // (X s> 13 | X == 15) -> X > 13
-    case ICmpInst::ICMP_SGT: // (X s> 13 | X s> 15) -> X > 13
-      return LHS;
-    case ICmpInst::ICMP_NE:  // (X s> 13 | X != 15) -> true
-    case ICmpInst::ICMP_SLT: // (X s> 13 | X s< 15) -> true
-      return Builder->getTrue();
     }
     break;
   }
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