From 5c6fc1cab774244fba2746b84f2b86d71b897733 Mon Sep 17 00:00:00 2001
From: Nick Lewycky <nicholas@mxc.ca>
Date: Wed, 19 Jan 2011 18:56:00 +0000
Subject: Similarly, analyze truncate through multiply.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@123842 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Analysis/ScalarEvolution.cpp      | 14 ++++++++++++++
 test/Analysis/ScalarEvolution/fold.ll |  8 ++++++++
 2 files changed, 22 insertions(+)

diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index 7258feca6c..424f74427b 100644
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -833,6 +833,20 @@ const SCEV *ScalarEvolution::getTruncateExpr(const SCEV *Op,
       return getAddExpr(Operands, false, false);
   }
 
+  // trunc(x1*x2*...*xN) --> trunc(x1)*trunc(x2)*...*trunc(xN) if we can
+  // eliminate all the 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);
+      Operands.push_back(S);
+    }
+    if (!hasTrunc)
+      return getMulExpr(Operands, false, false);
+  }
+
   // If the input value is a chrec scev, truncate the chrec's operands.
   if (const SCEVAddRecExpr *AddRec = dyn_cast<SCEVAddRecExpr>(Op)) {
     SmallVector<const SCEV *, 4> Operands;
diff --git a/test/Analysis/ScalarEvolution/fold.ll b/test/Analysis/ScalarEvolution/fold.ll
index f46c691f46..3c1b6ae0fe 100644
--- a/test/Analysis/ScalarEvolution/fold.ll
+++ b/test/Analysis/ScalarEvolution/fold.ll
@@ -14,3 +14,11 @@ define i8 @test2(i8 %x) {
 ; CHECK: (1 + %x)
   ret i8 %C
 }
+
+define i8 @test3(i8 %x) {
+  %A = zext i8 %x to i16
+  %B = mul i16 %A, 1027
+  %C = trunc i16 %B to i8
+; CHECK: (3 * %x)
+  ret i8 %C
+}
-- 
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