[llvm] r224676 - InstCombine: Squash an icmp+select into bitwise arithmetic

[David Majnemer]

Author: majnemer
Date: Fri Dec 19 22:45:35 2014
New Revision: 224676

URL: http://llvm.org/viewvc/llvm-project?rev=224676&view=rev
Log:
InstCombine: Squash an icmp+select into bitwise arithmetic

(X & INT_MIN) == 0 ? X ^ INT_MIN : X  into  X | INT_MIN
(X & INT_MIN) != 0 ? X ^ INT_MIN : X  into  X & INT_MAX

This fixes PR21993.

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=224676&r1=224675&r2=224676&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineSelect.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineSelect.cpp Fri Dec 19 22:45:35 2014
@@ -617,26 +617,44 @@ Instruction *InstCombiner::visitSelectIn
     }
   }
 
-  {
+  if (unsigned BitWidth = TrueVal->getType()->getScalarSizeInBits()) {
+    APInt MinSignedValue = APInt::getSignBit(BitWidth);
     Value *X;
     const APInt *Y, *C;
-    if (match(CmpLHS, m_And(m_Value(X), m_Power2(Y))) &&
+    bool TrueWhenUnset;
+    bool IsBitTest = false;
+    if (ICmpInst::isEquality(Pred) &&
+        match(CmpLHS, m_And(m_Value(X), m_Power2(Y))) &&
         match(CmpRHS, m_Zero())) {
+      IsBitTest = true;
+      TrueWhenUnset = Pred == ICmpInst::ICMP_EQ;
+    } else if (Pred == ICmpInst::ICMP_SLT && match(CmpRHS, m_Zero())) {
+      X = CmpLHS;
+      Y = &MinSignedValue;
+      IsBitTest = true;
+      TrueWhenUnset = false;
+    } else if (Pred == ICmpInst::ICMP_SGT && match(CmpRHS, m_AllOnes())) {
+      X = CmpLHS;
+      Y = &MinSignedValue;
+      IsBitTest = true;
+      TrueWhenUnset = true;
+    }
+    if (IsBitTest) {
       Value *V = nullptr;
       // (X & Y) == 0 ? X : X ^ Y  --> X & ~Y
-      if (Pred == ICmpInst::ICMP_EQ && TrueVal == X &&
+      if (TrueWhenUnset && TrueVal == X &&
           match(FalseVal, m_Xor(m_Specific(X), m_APInt(C))) && *Y == *C)
         V = Builder->CreateAnd(X, ~(*Y));
       // (X & Y) != 0 ? X ^ Y : X  --> X & ~Y
-      else if (Pred == ICmpInst::ICMP_NE && FalseVal == X &&
+      else if (!TrueWhenUnset && FalseVal == X &&
                match(TrueVal, m_Xor(m_Specific(X), m_APInt(C))) && *Y == *C)
         V = Builder->CreateAnd(X, ~(*Y));
       // (X & Y) == 0 ? X ^ Y : X  --> X | Y
-      else if (Pred == ICmpInst::ICMP_EQ && FalseVal == X &&
+      else if (TrueWhenUnset && FalseVal == X &&
                match(TrueVal, m_Xor(m_Specific(X), m_APInt(C))) && *Y == *C)
         V = Builder->CreateOr(X, *Y);
       // (X & Y) != 0 ? X : X ^ Y  --> X | Y
-      else if (Pred == ICmpInst::ICMP_NE && TrueVal == X &&
+      else if (!TrueWhenUnset && TrueVal == X &&
                match(FalseVal, m_Xor(m_Specific(X), m_APInt(C))) && *Y == *C)
         V = Builder->CreateOr(X, *Y);
 

Modified: llvm/trunk/test/Transforms/InstCombine/select.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/select.ll?rev=224676&r1=224675&r2=224676&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/select.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/select.ll Fri Dec 19 22:45:35 2014
@@ -1050,6 +1050,39 @@ define i64 @select_icmp_x_and_8_ne_0_y_o
   ret i64 %or.y
 }
 
+; CHECK-LABEL: @select_icmp_and_2147483648_ne_0_xor_2147483648(
+; CHECK-NEXT: [[AND:%[a-z0-9]+]] = and i32 %x, 2147483647
+; CHECK-NEXT: ret i32 [[AND]]
+define i32 @select_icmp_and_2147483648_ne_0_xor_2147483648(i32 %x) {
+  %and = and i32 %x, 2147483648
+  %cmp = icmp eq i32 %and, 0
+  %xor = xor i32 %x, 2147483648
+  %x.xor = select i1 %cmp, i32 %x, i32 %xor
+  ret i32 %x.xor
+}
+
+; CHECK-LABEL: @select_icmp_and_2147483648_eq_0_xor_2147483648(
+; CHECK-NEXT: [[OR:%[a-z0-9]+]] = or i32 %x, -2147483648
+; CHECK-NEXT: ret i32 [[OR]]
+define i32 @select_icmp_and_2147483648_eq_0_xor_2147483648(i32 %x) {
+  %and = and i32 %x, 2147483648
+  %cmp = icmp eq i32 %and, 0
+  %xor = xor i32 %x, 2147483648
+  %xor.x = select i1 %cmp, i32 %xor, i32 %x
+  ret i32 %xor.x
+}
+
+; CHECK-LABEL: @select_icmp_x_and_2147483648_ne_0_or_2147483648(
+; CHECK: xor i32 %1, -2147483648
+; CHECK: or i32 %2, %x
+define i32 @select_icmp_x_and_2147483648_ne_0_or_2147483648(i32 %x) {
+  %and = and i32 %x, 2147483648
+  %cmp = icmp eq i32 %and, 0
+  %or = or i32 %x, 2147483648
+  %or.x = select i1 %cmp, i32 %or, i32 %x
+  ret i32 %or.x
+}
+
 define i32 @test65(i64 %x) {
   %1 = and i64 %x, 16
   %2 = icmp ne i64 %1, 0