Also attempt trivial coalescing for live intervals that end in a copy.

The coalescer is supposed to clean these up, but when setting up parameters
for a function call, there may be copies to physregs. If the defining
instruction has been LICM'ed far away, the coalescer won't touch it.

The register allocation hint does not always work - when the register
allocator is backtracking, it clears the hints.

This patch is more conservative than r90502, and does not break
483.xalancbmk/i686. It still breaks the PowerPC bootstrap, so it is disabled
by default, and can be enabled with the -trivial-coalesce-ends option.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@91049 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 7 insertions, 4 deletions

diff --git a/include/llvm/CodeGen/LiveIntervalAnalysis.h b/include/llvm/CodeGen/LiveIntervalAnalysis.h
index a06e310..d7ff8da 100644
--- a/include/llvm/CodeGen/LiveIntervalAnalysis.h
+++ b/include/llvm/CodeGen/LiveIntervalAnalysis.h
@@ -112,10 +112,13 @@ namespace llvm {
       return (unsigned)(IntervalPercentage * indexes_->getFunctionSize());
     }
 
-    /// conflictsWithPhysRegDef - Returns true if the specified register
-    /// is defined during the duration of the specified interval.
-    bool conflictsWithPhysRegDef(const LiveInterval &li, VirtRegMap &vrm,
-                                 unsigned reg);
+    /// conflictsWithPhysReg - Returns true if the specified register is used or
+    /// defined during the duration of the specified interval. Copies to and
+    /// from li.reg are allowed. This method is only able to analyze simple
+    /// ranges that stay within a single basic block. Anything else is
+    /// considered a conflict.
+    bool conflictsWithPhysReg(const LiveInterval &li, VirtRegMap &vrm,
+                              unsigned reg);
 
     /// conflictsWithPhysRegRef - Similar to conflictsWithPhysRegRef except
     /// it can check use as well.