[llvm] r179748 - Combine bit test + conditional or into simple math

[David Majnemer]

Author: majnemer
Date: Thu Apr 18 02:30:07 2013
New Revision: 179748

URL: http://llvm.org/viewvc/llvm-project?rev=179748&view=rev
Log:
Combine bit test + conditional or into simple math

Simplify:
(select (icmp eq (and X, C1), 0), Y, (or Y, C2))

Into:
(or (shl (and X, C1), C3), y)

Where:
C3 = Log(C2) - Log(C1)

If:
C1 and C2 are both powers of two

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=179748&r1=179747&r2=179748&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineSelect.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineSelect.cpp Thu Apr 18 02:30:07 2013
@@ -350,6 +350,64 @@ static Value *SimplifyWithOpReplaced(Val
   return 0;
 }
 
+/// foldSelectICmpAndOr - We want to turn:
+///   (select (icmp eq (and X, C1), 0), Y, (or Y, C2))
+/// into:
+///   (or (shl (and X, C1), C3), y)
+/// iff:
+///   C1 and C2 are both powers of 2
+/// where:
+///   C3 = Log(C2) - Log(C1)
+///
+/// This transform handles cases where:
+/// 1. The icmp predicate is inverted
+/// 2. The select operands are reversed
+/// 3. The magnitude of C2 and C1 are flipped
+static Value *foldSelectICmpAndOr(const SelectInst &SI, Value *TrueVal,
+                                  Value *FalseVal,
+                                  InstCombiner::BuilderTy *Builder) {
+  const ICmpInst *IC = dyn_cast<ICmpInst>(SI.getCondition());
+  if (!IC || !IC->isEquality())
+    return 0;
+
+  Value *CmpLHS = IC->getOperand(0);
+  Value *CmpRHS = IC->getOperand(1);
+
+  if (!match(CmpRHS, m_Zero()))
+    return 0;
+
+  Value *X;
+  const APInt *C1;
+  if (!match(CmpLHS, m_And(m_Value(X), m_Power2(C1))))
+    return 0;
+
+  const APInt *C2;
+  bool OrOnTrueVal = false;
+  bool OrOnFalseVal = match(FalseVal, m_Or(m_Specific(TrueVal), m_Power2(C2)));
+  if (!OrOnFalseVal)
+    OrOnTrueVal = match(TrueVal, m_Or(m_Specific(FalseVal), m_Power2(C2)));
+
+  if (!OrOnFalseVal && !OrOnTrueVal)
+    return 0;
+
+  Value *V = CmpLHS;
+
+  unsigned C1Log = C1->logBase2();
+  unsigned C2Log = C2->logBase2();
+  if (C2Log > C1Log)
+    V = Builder->CreateShl(V, C2Log - C1Log);
+  else if (C1Log > C2Log)
+    V = Builder->CreateLShr(V, C1Log - C2Log);
+
+  ICmpInst::Predicate Pred = IC->getPredicate();
+  if ((Pred == ICmpInst::ICMP_NE && OrOnFalseVal) ||
+      (Pred == ICmpInst::ICMP_EQ && OrOnTrueVal))
+    V = Builder->CreateXor(V, *C2);
+
+  Value *Y = OrOnFalseVal ? TrueVal : FalseVal;
+  return Builder->CreateOr(V, Y);
+}
+
 /// visitSelectInstWithICmp - Visit a SelectInst that has an
 /// ICmpInst as its first operand.
 ///
@@ -521,6 +579,9 @@ Instruction *InstCombiner::visitSelectIn
     }
   }
 
+  if (Value *V = foldSelectICmpAndOr(SI, TrueVal, FalseVal, Builder))
+    return ReplaceInstUsesWith(SI, V);
+
   return Changed ? &SI : 0;
 }
 

Modified: llvm/trunk/test/Transforms/InstCombine/select.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/select.ll?rev=179748&r1=179747&r2=179748&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/select.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/select.ll Thu Apr 18 02:30:07 2013
@@ -863,3 +863,82 @@ while.body:
 ; CHECK: @test64
 ; CHECK-NOT: select
 }
+
+; CHECK: @select_icmp_eq_and_1_0_or_2
+; CHECK-NEXT: [[SHL:%[a-z0-9]+]] = shl i32 %x, 1
+; CHECK-NEXT: [[AND:%[a-z0-9]+]] = and i32 [[SHL]], 2
+; CHECK-NEXT: [[OR:%[a-z0-9]+]] = or i32 [[AND]], %y
+; CHECK-NEXT: ret i32 [[OR]]
+define i32 @select_icmp_eq_and_1_0_or_2(i32 %x, i32 %y) {
+  %and = and i32 %x, 1
+  %cmp = icmp eq i32 %and, 0
+  %or = or i32 %y, 2
+  %select = select i1 %cmp, i32 %y, i32 %or
+  ret i32 %select
+}
+
+; CHECK: @select_icmp_eq_and_32_0_or_8
+; CHECK-NEXT: [[LSHR:%[a-z0-9]+]] = lshr i32 %x, 2
+; CHECK-NEXT: [[AND:%[a-z0-9]+]] = and i32 [[LSHR]], 8
+; CHECK-NEXT: [[OR:%[a-z0-9]+]] = or i32 [[AND]], %y
+; CHECK-NEXT: ret i32 [[OR]]
+define i32 @select_icmp_eq_and_32_0_or_8(i32 %x, i32 %y) {
+  %and = and i32 %x, 32
+  %cmp = icmp eq i32 %and, 0
+  %or = or i32 %y, 8
+  %select = select i1 %cmp, i32 %y, i32 %or
+  ret i32 %select
+}
+
+; CHECK: @select_icmp_ne_0_and_4096_or_4096
+; CHECK-NEXT: [[AND:%[a-z0-9]+]] = and i32 %x, 4096
+; CHECK-NEXT: [[XOR:%[a-z0-9]+]] = xor i32 [[AND]], 4096
+; CHECK-NEXT: [[OR:%[a-z0-9]+]] = or i32 [[XOR]], %y
+; CHECK-NEXT: ret i32 [[OR]]
+define i32 @select_icmp_ne_0_and_4096_or_4096(i32 %x, i32 %y) {
+  %and = and i32 %x, 4096
+  %cmp = icmp ne i32 0, %and
+  %or = or i32 %y, 4096
+  %select = select i1 %cmp, i32 %y, i32 %or
+  ret i32 %select
+}
+
+; CHECK: @select_icmp_eq_and_4096_0_or_4096
+; CHECK-NEXT: [[AND:%[a-z0-9]+]] = and i32 %x, 4096
+; CHECK-NEXT: [[OR:%[a-z0-9]+]] = or i32 [[AND]], %y
+; CHECK-NEXT: ret i32 [[OR]]
+define i32 @select_icmp_eq_and_4096_0_or_4096(i32 %x, i32 %y) {
+  %and = and i32 %x, 4096
+  %cmp = icmp eq i32 %and, 0
+  %or = or i32 %y, 4096
+  %select = select i1 %cmp, i32 %y, i32 %or
+  ret i32 %select
+}
+
+; CHECK: @select_icmp_ne_0_and_4096_or_32
+; CHECK-NEXT: [[LSHR:%[a-z0-9]+]] = lshr i32 %x, 7
+; CHECK-NEXT: [[AND:%[a-z0-9]+]] = and i32 [[LSHR]], 32
+; CHECK-NEXT: [[XOR:%[a-z0-9]+]] = xor i32 [[AND]], 32
+; CHECK-NEXT: [[OR:%[a-z0-9]+]] = or i32 [[XOR]], %y
+; CHECK-NEXT: ret i32 [[OR]]
+define i32 @select_icmp_ne_0_and_4096_or_32(i32 %x, i32 %y) {
+  %and = and i32 %x, 4096
+  %cmp = icmp ne i32 0, %and
+  %or = or i32 %y, 32
+  %select = select i1 %cmp, i32 %y, i32 %or
+  ret i32 %select
+}
+
+; CHECK: @select_icmp_ne_0_and_32_or_4096
+; CHECK-NEXT: [[SHL:%[a-z0-9]+]] = shl i32 %x, 7
+; CHECK-NEXT: [[AND:%[a-z0-9]+]] = and i32 [[SHL]], 4096
+; CHECK-NEXT: [[XOR:%[a-z0-9]+]] = xor i32 [[AND]], 4096
+; CHECK-NEXT: [[OR:%[a-z0-9]+]] = or i32 [[XOR]], %y
+; CHECK-NEXT: ret i32 [[OR]]
+define i32 @select_icmp_ne_0_and_32_or_4096(i32 %x, i32 %y) {
+  %and = and i32 %x, 32
+  %cmp = icmp ne i32 0, %and
+  %or = or i32 %y, 4096
+  %select = select i1 %cmp, i32 %y, i32 %or
+  ret i32 %select
+}