[llvm-branch-commits] [llvm-branch] r196132 - Merging r196129:

[Bill Wendling]

Author: void
Date: Mon Dec  2 13:14:12 2013
New Revision: 196132

URL: http://llvm.org/viewvc/llvm-project?rev=196132&view=rev
Log:
Merging r196129:
------------------------------------------------------------------------
r196129 | kkhoo | 2013-12-02 10:43:59 -0800 (Mon, 02 Dec 2013) | 1 line

Conservative fix for PR17827 - don't optimize a shift + and + compare sequence where the shift is logical unless the comparison is unsigned
------------------------------------------------------------------------

Added:
    llvm/branches/release_34/test/Transforms/InstCombine/pr17827.ll
      - copied unchanged from r196129, llvm/trunk/test/Transforms/InstCombine/pr17827.ll
Modified:
    llvm/branches/release_34/   (props changed)
    llvm/branches/release_34/lib/Transforms/InstCombine/InstCombineCompares.cpp

Propchange: llvm/branches/release_34/
------------------------------------------------------------------------------
--- svn:mergeinfo (original)
+++ svn:mergeinfo Mon Dec  2 13:14:12 2013
@@ -1,3 +1,3 @@
 /llvm/branches/Apple/Pertwee:110850,110961
 /llvm/branches/type-system-rewrite:133420-134817
-/llvm/trunk:155241,195092-195094,195100,195102-195103,195118,195129,195136,195138,195148,195152,195156-195157,195161-195162,195193,195272,195317-195318,195327,195330,195333,195339,195343,195355,195364,195379,195397-195399,195401,195408,195421,195423-195424,195432,195439,195444,195455-195456,195469,195476-195477,195479,195491-195493,195514,195528,195547,195567,195573-195576,195590-195591,195599,195632,195635-195636,195670,195677,195679,195682,195684,195713,195716,195769,195773,195779,195782,195787-195788,195791,195803,195812,195827,195834,195843-195844,195878-195881,195887,195903,195905,195915,195932,195936-195943,195972-195973,195975-195976,196004,196044-196046
+/llvm/trunk:155241,195092-195094,195100,195102-195103,195118,195129,195136,195138,195148,195152,195156-195157,195161-195162,195193,195272,195317-195318,195327,195330,195333,195339,195343,195355,195364,195379,195397-195399,195401,195408,195421,195423-195424,195432,195439,195444,195455-195456,195469,195476-195477,195479,195491-195493,195514,195528,195547,195567,195573-195576,195590-195591,195599,195632,195635-195636,195670,195677,195679,195682,195684,195713,195716,195769,195773,195779,195782,195787-195788,195791,195803,195812,195827,195834,195843-195844,195878-195881,195887,195903,195905,195915,195932,195936-195943,195972-195973,195975-195976,196004,196044-196046,196129

Modified: llvm/branches/release_34/lib/Transforms/InstCombine/InstCombineCompares.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/branches/release_34/lib/Transforms/InstCombine/InstCombineCompares.cpp?rev=196132&r1=196131&r2=196132&view=diff
==============================================================================
--- llvm/branches/release_34/lib/Transforms/InstCombine/InstCombineCompares.cpp (original)
+++ llvm/branches/release_34/lib/Transforms/InstCombine/InstCombineCompares.cpp Mon Dec  2 13:14:12 2013
@@ -1198,11 +1198,16 @@ Instruction *InstCombiner::visitICmpInst
       Type *AndTy = AndCST->getType();          // Type of the and.
 
       // We can fold this as long as we can't shift unknown bits
-      // into the mask.  This can only happen with signed shift
-      // rights, as they sign-extend.
+      // into the mask. This can happen with signed shift
+      // rights, as they sign-extend. With logical shifts,
+      // we must still make sure the comparison is not signed
+      // because we are effectively changing the
+      // position of the sign bit (PR17827).
+      // TODO: We can relax these constraints a bit more.
       if (ShAmt) {
-        bool CanFold = Shift->isLogicalShift();
-        if (!CanFold) {
+        bool CanFold = false;
+        unsigned ShiftOpcode = Shift->getOpcode();
+        if (ShiftOpcode == Instruction::AShr) {
           // To test for the bad case of the signed shr, see if any
           // of the bits shifted in could be tested after the mask.
           uint32_t TyBits = Ty->getPrimitiveSizeInBits();
@@ -1212,6 +1217,9 @@ Instruction *InstCombiner::visitICmpInst
           if ((APInt::getHighBitsSet(BitWidth, BitWidth-ShAmtVal) &
                AndCST->getValue()) == 0)
             CanFold = true;
+        } else if (ShiftOpcode == Instruction::Shl ||
+                   ShiftOpcode == Instruction::LShr) {
+          CanFold = !ICI.isSigned();
         }
 
         if (CanFold) {