[llvm] r300746 - [SCEV] Make SCEV or modeling more aggressive.

[Eli Friedman via llvm-commits]

Author: efriedma
Date: Wed Apr 19 15:19:58 2017
New Revision: 300746

URL: http://llvm.org/viewvc/llvm-project?rev=300746&view=rev
Log:
[SCEV] Make SCEV or modeling more aggressive.

Use haveNoCommonBitsSet to figure out whether an "or" instruction
is equivalent to addition. This handles more cases than just
checking for a constant on the RHS.

Differential Revision: https://reviews.llvm.org/D32239


Added:
    llvm/trunk/test/Analysis/ScalarEvolution/or-as-add.ll
Modified:
    llvm/trunk/lib/Analysis/ScalarEvolution.cpp

Modified: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ScalarEvolution.cpp?rev=300746&r1=300745&r2=300746&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
+++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Wed Apr 19 15:19:58 2017
@@ -5328,28 +5328,12 @@ const SCEV *ScalarEvolution::createSCEV(
       break;
 
     case Instruction::Or:
-      // If the RHS of the Or is a constant, we may have something like:
-      // X*4+1 which got turned into X*4|1.  Handle this as an Add so loop
-      // optimizations will transparently handle this case.
-      //
-      // In order for this transformation to be safe, the LHS must be of the
-      // form X*(2^n) and the Or constant must be less than 2^n.
-      if (ConstantInt *CI = dyn_cast<ConstantInt>(BO->RHS)) {
-        const SCEV *LHS = getSCEV(BO->LHS);
-        const APInt &CIVal = CI->getValue();
-        if (GetMinTrailingZeros(LHS) >=
-            (CIVal.getBitWidth() - CIVal.countLeadingZeros())) {
-          // Build a plain add SCEV.
-          const SCEV *S = getAddExpr(LHS, getSCEV(CI));
-          // If the LHS of the add was an addrec and it has no-wrap flags,
-          // transfer the no-wrap flags, since an or won't introduce a wrap.
-          if (const SCEVAddRecExpr *NewAR = dyn_cast<SCEVAddRecExpr>(S)) {
-            const SCEVAddRecExpr *OldAR = cast<SCEVAddRecExpr>(LHS);
-            const_cast<SCEVAddRecExpr *>(NewAR)->setNoWrapFlags(
-                OldAR->getNoWrapFlags());
-          }
-          return S;
-        }
+      // Use ValueTracking to check whether this is actually an add.
+      if (haveNoCommonBitsSet(BO->LHS, BO->RHS, getDataLayout(), &AC,
+                              nullptr, &DT)) {
+        // There aren't any common bits set, so the add can't wrap.
+        auto Flags = SCEV::NoWrapFlags(SCEV::FlagNUW | SCEV::FlagNSW);
+        return getAddExpr(getSCEV(BO->LHS), getSCEV(BO->RHS), Flags);
       }
       break;
 

Added: llvm/trunk/test/Analysis/ScalarEvolution/or-as-add.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/ScalarEvolution/or-as-add.ll?rev=300746&view=auto
==============================================================================
--- llvm/trunk/test/Analysis/ScalarEvolution/or-as-add.ll (added)
+++ llvm/trunk/test/Analysis/ScalarEvolution/or-as-add.ll Wed Apr 19 15:19:58 2017
@@ -0,0 +1,38 @@
+; RUN: opt < %s -analyze -scalar-evolution | FileCheck %s
+
+declare void @z(i32)
+declare void @z2(i64)
+
+define void @fun(i1 %bool, i32 %x) {
+entry:
+        br label %body
+body:
+        %i = phi i32 [ 0, %entry ], [ %i.next, %body ]
+        %bottom_zero = mul i32 %i, 2
+        %a = or i32 %bottom_zero, 1
+        call void @z(i32 %a)
+        %bool_ext = zext i1 %bool to i32
+        %b = or i32 %bool_ext, %bottom_zero
+        call void @z(i32 %b)
+        %shifted = lshr i32 %x, 31
+        %c = or i32 %shifted, %bottom_zero
+        call void @z(i32 %c)
+        %i_ext = zext i32 %i to i64
+        %d = or i64 %i_ext, 4294967296
+        call void @z2(i64 %d)
+        %i.next = add i32 %i, 1
+        %cond = icmp eq i32 %i.next, 10
+        br i1 %cond, label %exit, label %body
+exit:
+        ret void
+}
+
+; CHECK: %a = or i32 %bottom_zero, 1
+; CHECK-NEXT: -->  {1,+,2}<%body>
+; CHECK: %b = or i32 %bool_ext, %bottom_zero
+; CHECK-NEXT: -->  {(zext i1 %bool to i32),+,2}
+; CHECK: %c = or i32 %shifted, %bottom_zero
+; CHECK-NEXT: -->  {(%x /u -2147483648),+,2}<%body>
+; CHECK: %d = or i64 %i_ext, 4294967296
+; CHECK-NEXT: -->  {4294967296,+,1}<nuw><nsw><%body>
+