[PATCH] D13756: sgt on i1s also encodes implication

[Philip Reames via llvm-commits]

This revision was automatically updated to reflect the committed changes.
Closed by commit rL251597: [InstSimplify] sgt on i1s also encodes implication (authored by reames).

Changed prior to commit:
  http://reviews.llvm.org/D13756?vs=37423&id=38707#toc

Repository:
  rL LLVM

http://reviews.llvm.org/D13756

Files:
  llvm/trunk/lib/Analysis/InstructionSimplify.cpp
  llvm/trunk/test/Transforms/InstSimplify/implies.ll

Index: llvm/trunk/test/Transforms/InstSimplify/implies.ll
===================================================================
--- llvm/trunk/test/Transforms/InstSimplify/implies.ll
+++ llvm/trunk/test/Transforms/InstSimplify/implies.ll
@@ -91,3 +91,14 @@
   %res = icmp ule <4 x i1> %a, %b
   ret <4 x i1> %res
 }
+
+; X >=(s) Y == X ==> Y (i1 1 becomes -1 for reasoning)
+define i1 @test_sge(i32 %length.i, i32 %i) {
+; CHECK-LABEL: @test_sge
+; CHECK: ret i1 true
+  %iplus1 = add nsw nuw i32 %i, 1
+  %var29 = icmp ult i32 %i, %length.i
+  %var30 = icmp ult i32 %iplus1, %length.i
+  %res = icmp sge i1 %var30, %var29
+  ret i1 %res
+}
Index: llvm/trunk/lib/Analysis/InstructionSimplify.cpp
===================================================================
--- llvm/trunk/lib/Analysis/InstructionSimplify.cpp
+++ llvm/trunk/lib/Analysis/InstructionSimplify.cpp
@@ -2179,6 +2179,17 @@
       if (isImpliedCondition(RHS, LHS))
         return getTrue(ITy);
       break;
+    case ICmpInst::ICMP_SGE:
+      /// For signed comparison, the values for an i1 are 0 and -1 
+      /// respectively. This maps into a truth table of:
+      /// LHS | RHS | LHS >=s RHS   | LHS implies RHS
+      ///  0  |  0  |  1 (0 >= 0)   |  1
+      ///  0  |  1  |  1 (0 >= -1)  |  1
+      ///  1  |  0  |  0 (-1 >= 0)  |  0
+      ///  1  |  1  |  1 (-1 >= -1) |  1
+      if (isImpliedCondition(LHS, RHS))
+        return getTrue(ITy);
+      break;
     case ICmpInst::ICMP_SLT:
       // X <s 0 -> X
       if (match(RHS, m_Zero()))


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