From: Shuxin Yang <shuxin.llvm@gmail.com>
Date: Tue, 4 Dec 2012 22:15:32 +0000 (+0000)
Subject:   For rdar://12329730, last piece.
X-Git-Url: http://plrg.eecs.uci.edu/git/?a=commitdiff_plain;h=a09e18fcfab0e998526724357f8fc5ef7f4c3e7a;p=oota-llvm.git

  For rdar://12329730, last piece.

  This change attempts to simplify (X^Y) -> X or Y in the user's context if we know that
only bits from X or Y are demanded.

  A minimized case is provided bellow. This change will simplify "t>>16" into "var1 >>16".

  =============================================================
  unsigned foo (unsigned val1, unsigned val2) {
    unsigned t = val1 ^ 1234;
    return (t >> 16) | t; // NOTE: t is used more than once.
  }
  =============================================================

  Note that if the "t" were used only once, the expression would be finally optimized as well.
However, with with this change, the optimization will take place earlier.

  Reviewed by Nadav, Thanks a lot!


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@169317 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
index c832ca5644a..08aedb3200a 100644
--- a/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ b/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -200,8 +200,21 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
       if ((DemandedMask & (~LHSKnownZero) & RHSKnownOne) == 
           (DemandedMask & (~LHSKnownZero)))
         return I->getOperand(1);
+    } else if (I->getOpcode() == Instruction::Xor) {
+      // We can simplify (X^Y) -> X or Y in the user's context if we know that
+      // only bits from X or Y are demanded.
+      
+      ComputeMaskedBits(I->getOperand(1), RHSKnownZero, RHSKnownOne, Depth+1);
+      ComputeMaskedBits(I->getOperand(0), LHSKnownZero, LHSKnownOne, Depth+1);
+      
+      // If all of the demanded bits are known zero on one side, return the
+      // other. 
+      if ((DemandedMask & RHSKnownZero) == DemandedMask)
+        return I->getOperand(0);
+      if ((DemandedMask & LHSKnownZero) == DemandedMask)
+        return I->getOperand(1);
     }
-    
+
     // Compute the KnownZero/KnownOne bits to simplify things downstream.
     ComputeMaskedBits(I, KnownZero, KnownOne, Depth);
     return 0;
diff --git a/test/Transforms/InstCombine/2010-11-01-lshr-mask.ll b/test/Transforms/InstCombine/2010-11-01-lshr-mask.ll
index 5efad8a789f..80016219791 100644
--- a/test/Transforms/InstCombine/2010-11-01-lshr-mask.ll
+++ b/test/Transforms/InstCombine/2010-11-01-lshr-mask.ll
@@ -5,8 +5,8 @@
 define i32 @main(i32 %argc) nounwind ssp {
 entry:
   %tmp3151 = trunc i32 %argc to i8
-; CHECK: %tmp3162 = shl i8 %tmp3151, 5
-; CHECK: and i8 %tmp3162, 64
+; CHECK: %0 = shl i8 %tmp3151, 5
+; CHECK: and i8 %0, 64
 ; CHECK-NOT: shl
 ; CHECK-NOT: shr
   %tmp3161 = or i8 %tmp3151, -17
diff --git a/test/Transforms/InstCombine/shift.ll b/test/Transforms/InstCombine/shift.ll
index fad0bd7ede3..32867761a3f 100644
--- a/test/Transforms/InstCombine/shift.ll
+++ b/test/Transforms/InstCombine/shift.ll
@@ -523,9 +523,9 @@ entry:
   %tmp51 = xor i8 %tmp50, %tmp5
   %tmp52 = and i8 %tmp51, -128
   %tmp53 = lshr i8 %tmp52, 7
-; CHECK: lshr i8 %tmp51, 7
   %tmp54 = mul i8 %tmp53, 16
-; CHECK: shl nuw nsw i8 %tmp53, 4
+; CHECK: %0 = shl i8 %tmp4, 2
+; CHECK: %tmp54 = and i8 %0, 16
   %tmp55 = xor i8 %tmp54, %tmp51
 ; CHECK: ret i8 %tmp551
   ret i8 %tmp55
diff --git a/test/Transforms/InstCombine/xor2.ll b/test/Transforms/InstCombine/xor2.ll
index 3c992467967..4ff3b1a4552 100644
--- a/test/Transforms/InstCombine/xor2.ll
+++ b/test/Transforms/InstCombine/xor2.ll
@@ -66,3 +66,19 @@ test5:
 ; CHECK: lshr i32 %val1, 8
 ; CHECK: ret
 }
+
+; defect-1 in rdar://12329730
+; Simplify (X^Y) -> X or Y in the user's context if we know that 
+; only bits from X or Y are demanded.
+; e.g. the "x ^ 1234" can be optimized into x in the context of "t >> 16".
+;  Put in other word, t >> 16 -> x >> 16.
+; unsigned foo(unsigned x) { nsigned t = x ^ 1234; ;  return (t >> 16) + t;}
+define i32 @test6(i32 %x) {
+  %xor = xor i32 %x, 1234
+  %shr = lshr i32 %xor, 16
+  %add = add i32 %shr, %xor
+  ret i32 %add
+; CHECK: @test6
+; CHECK: lshr i32 %x, 16
+; CHECK: ret
+}