From: Chris Lattner <sabre@nondot.org>
Date: Sat, 9 Apr 2011 06:57:13 +0000 (+0000)
Subject: Avoid excess precision issues that lead to generating host-compiler-specific code.
X-Git-Tag: android-x86-6.0-r1~964^2~1698
X-Git-Url: http://git.osdn.net/view?a=commitdiff_plain;h=c3e4e59d1017178fdff33d6e34635f498c98592f;p=android-x86%2Fexternal-llvm.git

Avoid excess precision issues that lead to generating host-compiler-specific code.
Switch lowering probably shouldn't be using FP for this.  This resolves PR9581.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@129199 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
index f751bb708e7..8fb881b2700 100644
--- a/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp
@@ -2019,9 +2019,13 @@ bool SelectionDAGBuilder::handleBTSplitSwitchCase(CaseRec& CR,
     APInt Range = ComputeRange(LEnd, RBegin);
     assert((Range - 2ULL).isNonNegative() &&
            "Invalid case distance");
-    double LDensity = (double)LSize.roundToDouble() /
+    // Use volatile double here to avoid excess precision issues on some hosts,
+    // e.g. that use 80-bit X87 registers.
+    volatile double LDensity =
+       (double)LSize.roundToDouble() /
                            (LEnd - First + 1ULL).roundToDouble();
-    double RDensity = (double)RSize.roundToDouble() /
+    volatile double RDensity =
+      (double)RSize.roundToDouble() /
                            (Last - RBegin + 1ULL).roundToDouble();
     double Metric = Range.logBase2()*(LDensity+RDensity);
     // Should always split in some non-trivial place