Attachment 44141 Details for Bug 34370 – Extend variable lifetimes to the start of the loop containing a def

[patch] Extend variable lifetimes to the start of the loop containing a def

0001-mesa-Extend-variable-lifetimes-to-the-start-of-the-l.patch (text/plain), 1.96 KB, created by Ian Romanick on 2011-03-04 14:38:14 UTC

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Creator: Ian Romanick

Created: 2011-03-04 14:38:14 UTC

Size: 1.96 KB

patch

obsolete

>From 1e5c784e48929c0da7e287fbc233a7d49391d619 Mon Sep 17 00:00:00 2001
>From: Ian Romanick <ian.d.romanick@intel.com>
>Date: Thu, 3 Mar 2011 14:46:46 -0800
>Subject: [PATCH] mesa: Extend variable lifetimes to the start of the loop containing a def
>
>Consider the following situation:
>
>1. The variable is defined in a loop.
>2. The variable has no other use inside the loop.
>3. The definition inside the loop is reachable outside the loop.
>
>The problem is that the register allocator only marks the live range for the
>variable as extending from the definition inside the loop to the use outside
>the loop.  The live interval should extend from the beginning of the loop to
>the use outside the loop.
>
>This patch extends the liveness interval back to the start of the loop
>containing the definition.  This fixes the test case at hand, but may
>still fail with nested loops where only the innermost loop contains a
>definition, and that definition is reachable outside all the loops.
>Moreover, this results in unnecessarily large liveness intervals for
>values only reachable inside the loop.
>
>The proper fix would likely require significant work. 
>---
> src/mesa/program/prog_optimize.c |   10 ++++++++++
> 1 files changed, 10 insertions(+), 0 deletions(-)
>
>diff --git a/src/mesa/program/prog_optimize.c b/src/mesa/program/prog_optimize.c
>index 96971f2..33eddcc 100644
>--- a/src/mesa/program/prog_optimize.c
>+++ b/src/mesa/program/prog_optimize.c
>@@ -956,6 +956,16 @@ update_interval(GLint intBegin[], GLint intEnd[],
>    else {
>       intEnd[index] = ic;
>    }
>+
>+   /* Extend the liveness interval to at least the beginning of the loop
>+    * containing this usage.  This seems to fix problems encountered when a
>+    * variable is defined (but not otherwise used) inside a loop, and that
>+    * definition is used outside the loop.
>+    */
>+   if (loopStackDepth > 0
>+       && intBegin[index] > loopStack[loopStackDepth - 1].Start) {
>+      intBegin[index] = loopStack[loopStackDepth - 1].Start;
>+   }
> }
> 
> 
>-- 
>1.7.4
>

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