[llvm] r368519 - [InstCombine] Shift amount reassociation in bittest: relax one-use check when shifting constant

[Roman Lebedev via llvm-commits]

Author: lebedevri
Date: Sat Aug 10 12:28:54 2019
New Revision: 368519

URL: http://llvm.org/viewvc/llvm-project?rev=368519&view=rev
Log:
[InstCombine] Shift amount reassociation in bittest: relax one-use check when shifting constant

If one of the values being shifted is a constant, since the new shift
amount is known-constant, the new shift will end up being constant-folded
so, we don't need that one-use restriction then.

Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
    llvm/trunk/test/Transforms/InstCombine/shift-amount-reassociation-in-bittest.ll

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp?rev=368519&r1=368518&r2=368519&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp Sat Aug 10 12:28:54 2019
@@ -3314,7 +3314,7 @@ foldShiftIntoShiftInAnotherHandOfAndInIC
   // Pick the single-use shift as XShift.
   Value *XShift, *YShift;
   if (!match(I.getOperand(0),
-             m_c_And(m_OneUse(m_CombineAnd(m_AnyLogicalShift, m_Value(XShift))),
+             m_c_And(m_CombineAnd(m_AnyLogicalShift, m_Value(XShift)),
                      m_CombineAnd(m_AnyLogicalShift, m_Value(YShift)))))
     return nullptr;
 
@@ -3332,6 +3332,16 @@ foldShiftIntoShiftInAnotherHandOfAndInIC
   match(XShift, m_BinOp(m_Value(X), m_Value(XShAmt)));
   match(YShift, m_BinOp(m_Value(Y), m_Value(YShAmt)));
 
+  // If one of the values being shifted is a constant, then we will end with
+  // and+icmp, and shift instr will be constant-folded. If they are not,
+  // however, we will need to ensure that we won't increase instruction count.
+  if (!isa<Constant>(X) && !isa<Constant>(Y)) {
+    // At least one of the hands of the 'and' should be one-use shift.
+    if (!match(I.getOperand(0),
+               m_c_And(m_OneUse(m_AnyLogicalShift), m_Value())))
+      return nullptr;
+  }
+
   // Can we fold (XShAmt+YShAmt) ?
   Value *NewShAmt = SimplifyBinOp(Instruction::BinaryOps::Add, XShAmt, YShAmt,
                                   SQ.getWithInstruction(&I));

Modified: llvm/trunk/test/Transforms/InstCombine/shift-amount-reassociation-in-bittest.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/shift-amount-reassociation-in-bittest.ll?rev=368519&r1=368518&r2=368519&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/shift-amount-reassociation-in-bittest.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/shift-amount-reassociation-in-bittest.ll Sat Aug 10 12:28:54 2019
@@ -534,9 +534,9 @@ define i1 @t32_shift_of_const_oneuse0(i3
 ; CHECK-NEXT:    call void @use32(i32 [[T2]])
 ; CHECK-NEXT:    [[T3:%.*]] = shl i32 [[Y:%.*]], [[T2]]
 ; CHECK-NEXT:    call void @use32(i32 [[T3]])
-; CHECK-NEXT:    [[T4:%.*]] = and i32 [[T1]], [[T3]]
-; CHECK-NEXT:    [[T5:%.*]] = icmp ne i32 [[T4]], 0
-; CHECK-NEXT:    ret i1 [[T5]]
+; CHECK-NEXT:    [[TMP1:%.*]] = and i32 [[Y]], 1
+; CHECK-NEXT:    [[TMP2:%.*]] = icmp ne i32 [[TMP1]], 0
+; CHECK-NEXT:    ret i1 [[TMP2]]
 ;
   %t0 = sub i32 32, %len
   call void @use32(i32 %t0)
@@ -561,9 +561,7 @@ define i1 @t33_shift_of_const_oneuse1(i3
 ; CHECK-NEXT:    call void @use32(i32 [[T2]])
 ; CHECK-NEXT:    [[T3:%.*]] = shl i32 -52543054, [[T2]]
 ; CHECK-NEXT:    call void @use32(i32 [[T3]])
-; CHECK-NEXT:    [[T4:%.*]] = and i32 [[T1]], [[T3]]
-; CHECK-NEXT:    [[T5:%.*]] = icmp ne i32 [[T4]], 0
-; CHECK-NEXT:    ret i1 [[T5]]
+; CHECK-NEXT:    ret i1 false
 ;
   %t0 = sub i32 32, %len
   call void @use32(i32 %t0)