[llvm-commits] [llvm] r94745 - in /llvm/trunk: lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp test/Transforms/InstCombine/2010-01-28-NegativeSRem.ll

[Duncan Sands]

Author: baldrick
Date: Thu Jan 28 11:22:42 2010
New Revision: 94745

URL: http://llvm.org/viewvc/llvm-project?rev=94745&view=rev
Log:
Fix PR6165.  The bug was that LHSKnownZero was being and'd with DemandedMask
when it should have been and'd with LowBits.  Fix that and while there beef
up the logic in the case of a negative LHS.

Added:
    llvm/trunk/test/Transforms/InstCombine/2010-01-28-NegativeSRem.ll
Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp?rev=94745&r1=94744&r2=94745&view=diff

==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp Thu Jan 28 11:22:42 2010
@@ -681,10 +681,19 @@
                                  LHSKnownZero, LHSKnownOne, Depth+1))
           return I;
 
+        // The low bits of LHS are unchanged by the srem.
+        KnownZero |= LHSKnownZero & LowBits;
+        KnownOne |= LHSKnownOne & LowBits;
+
+        // If LHS is non-negative or has all low bits zero, then the upper bits
+        // are all zero.
         if (LHSKnownZero[BitWidth-1] || ((LHSKnownZero & LowBits) == LowBits))
-          LHSKnownZero |= ~LowBits;
+          KnownZero |= ~LowBits;
 
-        KnownZero |= LHSKnownZero & DemandedMask;
+        // If LHS is negative and not all low bits are zero, then the upper bits
+        // are all one.
+        if (LHSKnownOne[BitWidth-1] && ((LHSKnownOne & LowBits) != 0))
+          KnownOne |= ~LowBits;
 
         assert(!(KnownZero & KnownOne) && "Bits known to be one AND zero?"); 
       }

Added: llvm/trunk/test/Transforms/InstCombine/2010-01-28-NegativeSRem.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/2010-01-28-NegativeSRem.ll?rev=94745&view=auto

==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/2010-01-28-NegativeSRem.ll (added)
+++ llvm/trunk/test/Transforms/InstCombine/2010-01-28-NegativeSRem.ll Thu Jan 28 11:22:42 2010
@@ -0,0 +1,19 @@
+; RUN: opt < %s -instcombine -S | FileCheck %s
+; PR6165
+
+define i32 @f() {
+entry:
+  br label %BB1
+
+BB1:                                              ; preds = %BB1, %entry
+; CHECK: BB1:
+  %x = phi i32 [ -29, %entry ], [ 0, %BB1 ]       ; <i32> [#uses=2]
+  %rem = srem i32 %x, 2                           ; <i32> [#uses=1]
+  %t = icmp eq i32 %rem, -1                       ; <i1> [#uses=1]
+  br i1 %t, label %BB2, label %BB1
+; CHECK-NOT: br i1 false
+
+BB2:                                              ; preds = %BB1
+; CHECK: BB2:
+  ret i32 %x
+}