implement an instcombine xform needed by clang's codegen

on the example in PR4216.  This doesn't trigger in the testsuite,
so I'd really appreciate someone scrutinizing the logic for
correctness.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@92458 91177308-0d34-0410-b5e6-96231b3b80d8

3 files changed, 32 insertions, 14 deletions

diff --git a/lib/Target/README.txt b/lib/Target/README.txt
index a6e05fadef..22dadfeb3d 100644
--- a/lib/Target/README.txt
+++ b/lib/Target/README.txt
@@ -282,19 +282,6 @@ this requires TBAA.
 
 //===---------------------------------------------------------------------===//
 
-This should be optimized to one 'and' and one 'or', from PR4216:
-
-define i32 @test_bitfield(i32 %bf.prev.low) nounwind ssp {
-entry:
-  %bf.prev.lo.cleared10 = or i32 %bf.prev.low, 32962 ; <i32> [#uses=1]
-  %0 = and i32 %bf.prev.low, -65536               ; <i32> [#uses=1]
-  %1 = and i32 %bf.prev.lo.cleared10, 40186       ; <i32> [#uses=1]
-  %2 = or i32 %1, %0                              ; <i32> [#uses=1]
-  ret i32 %2
-}
-
-//===---------------------------------------------------------------------===//
-
 This isn't recognized as bswap by instcombine (yes, it really is bswap):
 
 unsigned long reverse(unsigned v) {
diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index 363d8798f3..03885a5e05 100644
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -5213,12 +5213,30 @@ Instruction *InstCombiner::visitOr(BinaryOperator &I) {
             return ReplaceInstUsesWith(I, B);
         }
       }
-      V1 = 0; V2 = 0; V3 = 0;
+      
+      // ((V | N) & C1) | (V & C2) --> (V|N) & (C1|C2)
+      // iff (C1&C2) == 0 and (N&~C1) == 0
+      if ((C1->getValue() & C2->getValue()) == 0) {
+        if (match(A, m_Or(m_Value(V1), m_Value(V2))) &&
+            ((V1 == B && MaskedValueIsZero(V2, ~C1->getValue())) ||  // (V|N)
+             (V2 == B && MaskedValueIsZero(V1, ~C1->getValue()))))   // (N|V)
+          return BinaryOperator::CreateAnd(A,
+                               ConstantInt::get(A->getContext(),
+                                                C1->getValue()|C2->getValue()));
+        // Or commutes, try both ways.
+        if (match(B, m_Or(m_Value(V1), m_Value(V2))) &&
+            ((V1 == A && MaskedValueIsZero(V2, ~C2->getValue())) ||  // (V|N)
+             (V2 == A && MaskedValueIsZero(V1, ~C2->getValue()))))   // (N|V)
+          return BinaryOperator::CreateAnd(B,
+                               ConstantInt::get(B->getContext(),
+                                                C1->getValue()|C2->getValue()));
+      }
     }
     
     // Check to see if we have any common things being and'ed.  If so, find the
     // terms for V1 & (V2|V3).
     if (isOnlyUse(Op0) || isOnlyUse(Op1)) {
+      V1 = 0;
       if (A == B)      // (A & C)|(A & D) == A & (C|D)
         V1 = A, V2 = C, V3 = D;
       else if (A == D) // (A & C)|(B & A) == A & (B|C)
diff --git a/test/Transforms/InstCombine/or.ll b/test/Transforms/InstCombine/or.ll
index 44228ba357..822dfb3d55 100644
--- a/test/Transforms/InstCombine/or.ll
+++ b/test/Transforms/InstCombine/or.ll
@@ -307,3 +307,16 @@ define i1 @test29(i32* %A, i32* %B) {
 ; CHECK: ret i1
 }
 
+; PR4216
+define i32 @test30(i32 %A) {
+entry:
+  %B = or i32 %A, 32962
+  %C = and i32 %A, -65536
+  %D = and i32 %B, 40186
+  %E = or i32 %D, %C
+  ret i32 %E
+; CHECK: @test30
+; CHECK: %B = or i32 %A, 32962
+; CHECK: %E = and i32 %B, -25350
+; CHECK: ret i32 %E
+}