[llvm-commits] [llvm] r65364 - in /llvm/trunk: lib/Analysis/ValueTracking.cpp lib/CodeGen/SelectionDAG/SelectionDAG.cpp lib/Transforms/Scalar/InstructionCombining.cpp test/Transforms/InstCombine/ashr-nop.ll

[Dan Gohman]

Author: djg
Date: Mon Feb 23 20:00:40 2009
New Revision: 65364

URL: http://llvm.org/viewvc/llvm-project?rev=65364&view=rev
Log:
Fix a ValueTracking rule: RHS means operand 1, not 0. Add a simple
ashr instcombine to help expose this code. And apply the fix to
SelectionDAG's copy of this code too.

Added:
    llvm/trunk/test/Transforms/InstCombine/ashr-nop.ll
Modified:
    llvm/trunk/lib/Analysis/ValueTracking.cpp
    llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
    llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp

Modified: llvm/trunk/lib/Analysis/ValueTracking.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ValueTracking.cpp?rev=65364&r1=65363&r2=65364&view=diff

==============================================================================
--- llvm/trunk/lib/Analysis/ValueTracking.cpp (original)
+++ llvm/trunk/lib/Analysis/ValueTracking.cpp Mon Feb 23 20:00:40 2009
@@ -625,7 +625,7 @@
     if (Tmp == 1) return 1;  // Early out.
       
     // Special case decrementing a value (ADD X, -1):
-    if (ConstantInt *CRHS = dyn_cast<ConstantInt>(U->getOperand(0)))
+    if (ConstantInt *CRHS = dyn_cast<ConstantInt>(U->getOperand(1)))
       if (CRHS->isAllOnesValue()) {
         APInt KnownZero(TyBits, 0), KnownOne(TyBits, 0);
         APInt Mask = APInt::getAllOnesValue(TyBits);

Modified: llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp?rev=65364&r1=65363&r2=65364&view=diff

==============================================================================
--- llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/SelectionDAG.cpp Mon Feb 23 20:00:40 2009
@@ -2008,7 +2008,7 @@
     if (Tmp == 1) return 1;  // Early out.
 
     // Special case decrementing a value (ADD X, -1):
-    if (ConstantSDNode *CRHS = dyn_cast<ConstantSDNode>(Op.getOperand(0)))
+    if (ConstantSDNode *CRHS = dyn_cast<ConstantSDNode>(Op.getOperand(1)))
       if (CRHS->isAllOnesValue()) {
         APInt KnownZero, KnownOne;
         APInt Mask = APInt::getAllOnesValue(VTBits);

Modified: llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp?rev=65364&r1=65363&r2=65364&view=diff

==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp Mon Feb 23 20:00:40 2009
@@ -7031,7 +7031,12 @@
       MaskedValueIsZero(Op0,
                       APInt::getSignBit(I.getType()->getPrimitiveSizeInBits())))
     return BinaryOperator::CreateLShr(Op0, I.getOperand(1));
-  
+
+  // Arithmetic shifting an all-sign-bit value is a no-op.
+  unsigned NumSignBits = ComputeNumSignBits(Op0);
+  if (NumSignBits == Op0->getType()->getPrimitiveSizeInBits())
+    return ReplaceInstUsesWith(I, Op0);
+
   return 0;
 }
 

Added: llvm/trunk/test/Transforms/InstCombine/ashr-nop.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/ashr-nop.ll?rev=65364&view=auto

==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/ashr-nop.ll (added)
+++ llvm/trunk/test/Transforms/InstCombine/ashr-nop.ll Mon Feb 23 20:00:40 2009
@@ -0,0 +1,8 @@
+; RUN: llvm-as < %s | opt -instcombine | llvm-dis | not grep ashr
+
+define i32 @foo(i32 %x) {
+  %o = and i32 %x, 1
+  %n = add i32 %o, -1
+  %t = ashr i32 %n, 17
+  ret i32 %t
+}