From bea9b06e84c182d9e91e370c25e2a72af7b0008a Mon Sep 17 00:00:00 2001
From: Nick Lewycky <nicholas@mxc.ca>
Date: Fri, 20 Mar 2015 02:25:00 +0000
Subject: [PATCH] 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!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@232794 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Analysis/ScalarEvolution.cpp      | 10 ++++++----
 test/Analysis/ScalarEvolution/fold.ll | 12 ++++++++++++
 2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index a2d99a6ef0c..cbc8a45a709 100644
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -1102,13 +1102,14 @@ const SCEV *ScalarEvolution::getTruncateExpr(const SCEV *Op,
     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::getTruncateExpr(const SCEV *Op,
   }
 
   // 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)
diff --git a/test/Analysis/ScalarEvolution/fold.ll b/test/Analysis/ScalarEvolution/fold.ll
index 9b11b709951..226a24ff9c8 100644
--- a/test/Analysis/ScalarEvolution/fold.ll
+++ b/test/Analysis/ScalarEvolution/fold.ll
@@ -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
+}
-- 
2.34.1