[llvm] r252332 - [ValueTracking] De-pessimize isImpliedCondition around unsigned compares

[Sanjoy Das via llvm-commits]

Author: sanjoy
Date: Fri Nov  6 13:01:03 2015
New Revision: 252332

URL: http://llvm.org/viewvc/llvm-project?rev=252332&view=rev
Log:
[ValueTracking] De-pessimize isImpliedCondition around unsigned compares

Summary:
Currently `isImpliedCondition` will optimize "I +_nuw C < L ==> I < L"
only if C is positive.  This is an unnecessary restriction -- the
implication holds even if `C` is negative.

Reviewers: reames, majnemer

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D14369

Modified:
    llvm/trunk/lib/Analysis/ValueTracking.cpp
    llvm/trunk/test/Transforms/InstSimplify/implies.ll

Modified: llvm/trunk/lib/Analysis/ValueTracking.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ValueTracking.cpp?rev=252332&r1=252331&r2=252332&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ValueTracking.cpp (original)
+++ llvm/trunk/lib/Analysis/ValueTracking.cpp Fri Nov  6 13:01:03 2015
@@ -4109,12 +4109,12 @@ static bool isTruePredicate(CmpInst::Pre
   case CmpInst::ICMP_ULE: {
     ConstantInt *CI;
 
-    // LHS u<  LHS +_{nuw} C   if C > 0
-    // LHS u<= LHS +_{nuw} C   if C >= 0
+    // LHS u<  LHS +_{nuw} C   if C != 0
+    // LHS u<= LHS +_{nuw} C
     if (match(RHS, m_NUWAdd(m_Specific(LHS), m_ConstantInt(CI)))) {
       if (Pred == CmpInst::ICMP_ULT)
-        return CI->getValue().isStrictlyPositive();
-      return !CI->isNegative();
+        return !CI->isZero();
+      return true;
     }
     return false;
   }

Modified: llvm/trunk/test/Transforms/InstSimplify/implies.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstSimplify/implies.ll?rev=252332&r1=252331&r2=252332&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstSimplify/implies.ll (original)
+++ llvm/trunk/test/Transforms/InstSimplify/implies.ll Fri Nov  6 13:01:03 2015
@@ -65,7 +65,7 @@ define i1 @test3(i32 %length.i, i32 %i)
   ret i1 %res
 }
 
-; i +_{nuw} C_{>0} <u L ==> i <u L
+; i +_{nuw} C <u L ==> i <u L
 define i1 @test4(i32 %length.i, i32 %i) {
 ; CHECK-LABEL: @test4
 ; CHECK: ret i1 true
@@ -114,6 +114,17 @@ define i1 @test8(i32 %length.i, i32 %i)
   %var30 = icmp ult i32 %iplus1, %length.i
   %res = icmp ule i1 %var30, %var29
   ret i1 %res
+}
+
+; i +_{nuw} C <s L ==> i < L, even if C is negative
+define i1 @test9(i32 %length.i, i32 %i) {
+; CHECK-LABEL: @test9(
+; CHECK: ret i1 true
+  %iplus1 = add nuw i32 %i, -100
+  %var29 = icmp ult i32 %i, %length.i
+  %var30 = icmp ult i32 %iplus1, %length.i
+  %res = icmp ule i1 %var30, %var29
+  ret i1 %res
 }
 
 ; X >=(s) Y == X ==> Y (i1 1 becomes -1 for reasoning)