[llvm] r258904 - [SimplifyCFG] Don't mistake icmp of and for a tree of comparisons

[David Majnemer via llvm-commits]

Author: majnemer
Date: Tue Jan 26 20:43:28 2016
New Revision: 258904

URL: http://llvm.org/viewvc/llvm-project?rev=258904&view=rev
Log:
[SimplifyCFG] Don't mistake icmp of and for a tree of comparisons

SimplifyCFG tries to turn complex branch conditions into a switch.
Some of it's logic attempts to reason about bitwise arithmetic produced
by InstCombine.  InstCombine can turn things like (X == 2) || (X == 3)
into (X & 1) == 2 and so SimplifyCFG tries to detect when this occurs so
that it can produce a switch instruction.

However, the legality checking was not sufficient to determine whether
or not this had occured.  Correctly check this case by requiring that
the right-hand side of the comparison be a power of two.

This fixes PR26323.

Modified:
    llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
    llvm/trunk/test/Transforms/SimplifyCFG/switch_create.ll

Modified: llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp?rev=258904&r1=258903&r2=258904&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/SimplifyCFG.cpp Tue Jan 26 20:43:28 2016
@@ -405,13 +405,14 @@ private:
     ConstantInt *RHSC;
 
     // Pattern match a special case
-    // (x & ~2^x) == y --> x == y || x == y|2^x
+    // (x & ~2^z) == y --> x == y || x == y|2^z
     // This undoes a transformation done by instcombine to fuse 2 compares.
     if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ:ICmpInst::ICMP_NE)) {
       if (match(ICI->getOperand(0),
                 m_And(m_Value(RHSVal), m_ConstantInt(RHSC)))) {
         APInt Not = ~RHSC->getValue();
-        if (Not.isPowerOf2()) {
+        if (Not.isPowerOf2() && C->getValue().isPowerOf2() &&
+            Not != C->getValue()) {
           // If we already have a value for the switch, it has to match!
           if(!setValueOnce(RHSVal))
             return false;

Modified: llvm/trunk/test/Transforms/SimplifyCFG/switch_create.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/SimplifyCFG/switch_create.ll?rev=258904&r1=258903&r2=258904&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/SimplifyCFG/switch_create.ll (original)
+++ llvm/trunk/test/Transforms/SimplifyCFG/switch_create.ll Tue Jan 26 20:43:28 2016
@@ -554,3 +554,28 @@ bb20:
 ; CHECK: %arg.off = add i32 %arg, -8
 ; CHECK: icmp ult i32 %arg.off, 11
 }
+
+define void @PR26323(i1 %tobool23, i32 %tmp3) {
+entry:
+  %tobool5 = icmp ne i32 %tmp3, 0
+  %neg14 = and i32 %tmp3, -2
+  %cmp17 = icmp ne i32 %neg14, -1
+  %or.cond = and i1 %tobool5, %tobool23
+  %or.cond1 = and i1 %cmp17, %or.cond
+  br i1 %or.cond1, label %if.end29, label %if.then27
+
+if.then27:                                        ; preds = %entry
+  call void @foo1()
+  unreachable
+
+if.end29:                                         ; preds = %entry
+  ret void
+}
+
+; CHECK-LABEL: define void @PR26323(
+; CHECK:  %tobool5 = icmp ne i32 %tmp3, 0
+; CHECK:  %neg14 = and i32 %tmp3, -2
+; CHECK:  %cmp17 = icmp ne i32 %neg14, -1
+; CHECK:  %or.cond = and i1 %tobool5, %tobool23
+; CHECK:  %or.cond1 = and i1 %cmp17, %or.cond
+; CHECK:  br i1 %or.cond1, label %if.end29, label %if.then27