[llvm] r236202 - [InstCombine] Add a new formula for SMIN.

[Sanjoy Das]

Author: sanjoy
Date: Wed Apr 29 23:56:00 2015
New Revision: 236202

URL: http://llvm.org/viewvc/llvm-project?rev=236202&view=rev
Log:
[InstCombine] Add a new formula for SMIN.

Summary:
After this change `MatchSelectPattern` recognizes the following form
of SMIN:

  Y >s C ? ~Y : ~C == ~Y <s ~C ? ~Y : ~C = SMIN(~Y, ~C)

Reviewers: majnemer

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D9352

Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineSelect.cpp
    llvm/trunk/test/Transforms/InstCombine/select.ll

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineSelect.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineSelect.cpp?rev=236202&r1=236201&r2=236202&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineSelect.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineSelect.cpp Wed Apr 29 23:56:00 2015
@@ -86,6 +86,17 @@ MatchSelectPattern(Value *V, Value *&LHS
         return (CmpLHS == FalseVal) ? SPF_ABS : SPF_NABS;
       }
     }
+
+    // Y >s C ? ~Y : ~C == ~Y <s ~C ? ~Y : ~C = SMIN(~Y, ~C)
+    if (const auto *C2 = dyn_cast<ConstantInt>(FalseVal)) {
+      if (C1->getType() == C2->getType() && ~C1->getValue() == C2->getValue() &&
+          (match(TrueVal, m_Not(m_Specific(CmpLHS))) ||
+           match(CmpLHS, m_Not(m_Specific(TrueVal))))) {
+        LHS = TrueVal;
+        RHS = FalseVal;
+        return SPF_SMIN;
+      }
+    }
   }
 
   // TODO: (X > 4) ? X : 5   -->  (X >= 5) ? X : 5  -->  MAX(X, 5)

Modified: llvm/trunk/test/Transforms/InstCombine/select.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/select.ll?rev=236202&r1=236201&r2=236202&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/select.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/select.ll Wed Apr 29 23:56:00 2015
@@ -1520,3 +1520,15 @@ define i32 @test_select_select1(i32 %a,
   %s1 = select i1 %c1, i32 %r0, i32 %s0
   ret i32 %s1
 }
+
+define i32 @test_max_of_min(i32 %a) {
+; MAX(MIN(%a, -1), -1) == -1
+; CHECK-LABEL: @test_max_of_min(
+; CHECK: ret i32 -1
+  %not_a = xor i32 %a, -1
+  %c0 = icmp sgt i32 %a, 0
+  %s0 = select i1 %c0, i32 %not_a, i32 -1
+  %c1 = icmp sgt i32 %s0, -1
+  %s1 = select i1 %c1, i32 %s0, i32 -1
+  ret i32 %s1
+}