[llvm] r232794 - When simplifying a SCEV truncate by distributing, consider it a simplification to replace a cast, even if we end up with a trunc around the term. Fixes PR22960!

[Nick Lewycky]

Author: nicholas
Date: Thu Mar 19 21:25:00 2015
New Revision: 232794

URL: http://llvm.org/viewvc/llvm-project?rev=232794&view=rev
Log:
When simplifying a SCEV truncate by distributing, consider it a simplification to replace a cast, even if we end up with a trunc around the term. Fixes PR22960!

Modified:
    llvm/trunk/lib/Analysis/ScalarEvolution.cpp
    llvm/trunk/test/Analysis/ScalarEvolution/fold.ll

Modified: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ScalarEvolution.cpp?rev=232794&r1=232793&r2=232794&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
+++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Thu Mar 19 21:25:00 2015
@@ -1102,13 +1102,14 @@ const SCEV *ScalarEvolution::getTruncate
     return getTruncateOrZeroExtend(SZ->getOperand(), Ty);
 
   // trunc(x1+x2+...+xN) --> trunc(x1)+trunc(x2)+...+trunc(xN) if we can
-  // eliminate all the truncates.
+  // eliminate all the truncates, or we replace extensions with truncates.
   if (const SCEVAddExpr *SA = dyn_cast<SCEVAddExpr>(Op)) {
     SmallVector<const SCEV *, 4> Operands;
     bool hasTrunc = false;
     for (unsigned i = 0, e = SA->getNumOperands(); i != e && !hasTrunc; ++i) {
       const SCEV *S = getTruncateExpr(SA->getOperand(i), Ty);
-      hasTrunc = isa<SCEVTruncateExpr>(S);
+      if (!isa<SCEVCastExpr>(SA->getOperand(i)))
+        hasTrunc = isa<SCEVTruncateExpr>(S);
       Operands.push_back(S);
     }
     if (!hasTrunc)
@@ -1117,13 +1118,14 @@ const SCEV *ScalarEvolution::getTruncate
   }
 
   // trunc(x1*x2*...*xN) --> trunc(x1)*trunc(x2)*...*trunc(xN) if we can
-  // eliminate all the truncates.
+  // eliminate all the truncates, or we replace other casts with truncates.
   if (const SCEVMulExpr *SM = dyn_cast<SCEVMulExpr>(Op)) {
     SmallVector<const SCEV *, 4> Operands;
     bool hasTrunc = false;
     for (unsigned i = 0, e = SM->getNumOperands(); i != e && !hasTrunc; ++i) {
       const SCEV *S = getTruncateExpr(SM->getOperand(i), Ty);
-      hasTrunc = isa<SCEVTruncateExpr>(S);
+      if (!isa<SCEVCastExpr>(SM->getOperand(i)))
+        hasTrunc = isa<SCEVTruncateExpr>(S);
       Operands.push_back(S);
     }
     if (!hasTrunc)

Modified: llvm/trunk/test/Analysis/ScalarEvolution/fold.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/ScalarEvolution/fold.ll?rev=232794&r1=232793&r2=232794&view=diff
==============================================================================
--- llvm/trunk/test/Analysis/ScalarEvolution/fold.ll (original)
+++ llvm/trunk/test/Analysis/ScalarEvolution/fold.ll Thu Mar 19 21:25:00 2015
@@ -86,3 +86,15 @@ define void @test6(i8 %x) {
 ; CHECK: -->  (2048 * ((zext i8 %x to i16) /u 8))
   ret void
 }
+
+; PR22960
+define void @test7(i32 %A) {
+; CHECK-LABEL: @test7
+  %B = sext i32 %A to i64
+  %C = zext i32 %A to i64
+  %D = sub i64 %B, %C
+  %E = trunc i64 %D to i16
+; CHECK: %E
+; CHECK-NEXT: -->  0
+  ret void
+}