[llvm] r300928 - Revert r300746 (SCEV analysis for or instructions).

[Eli Friedman via llvm-commits]

Author: efriedma
Date: Thu Apr 20 18:59:05 2017
New Revision: 300928

URL: http://llvm.org/viewvc/llvm-project?rev=300928&view=rev
Log:
Revert r300746 (SCEV analysis for or instructions).

There have been multiple reports of this causing problems: a
compile-time explosion on the LLVM testsuite, and a stack
overflow for an opencl kernel.


Removed:
    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=300928&r1=300927&r2=300928&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
+++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Thu Apr 20 18:59:05 2017
@@ -5328,12 +5328,28 @@ const SCEV *ScalarEvolution::createSCEV(
       break;
 
     case Instruction::Or:
-      // 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);
+      // 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;
+        }
       }
       break;
 

Removed: 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=300927&view=auto
==============================================================================
--- llvm/trunk/test/Analysis/ScalarEvolution/or-as-add.ll (original)
+++ llvm/trunk/test/Analysis/ScalarEvolution/or-as-add.ll (removed)
@@ -1,38 +0,0 @@
-; 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>
-