[CodeGenPrepare] Check that erased sunken address are not reused

CodeGenPrepare sinks address computations from one basic block to another
and attempts to reuse address computations that have already been sunk. If
the same address computation appears twice with the first instance as an
operand of a load whose result is an operand to a simplifable select,
CodeGenPrepare simplifies the select and recursively erases the now dead
instructions. CodeGenPrepare then attempts to use the erased address
computation for the second load.

Fix this by erasing the cached address value if it has zero uses before
looking for the address value in the sunken address map.

This partially resolves PR35209.

Thanks to Alexander Richardson for reporting the issue!

Reviewers: john.brawn

Differential Revision: https://reviews.llvm.org/D39841

llvm-svn: 318032

1 files changed, 6 insertions, 1 deletions

diff --git a/llvm/lib/CodeGen/CodeGenPrepare.cpp b/llvm/lib/CodeGen/CodeGenPrepare.cpp
index d6633a508f5..96b7704a765 100644
--- a/llvm/lib/CodeGen/CodeGenPrepare.cpp
+++ b/llvm/lib/CodeGen/CodeGenPrepare.cpp
@@ -4358,7 +4358,12 @@ bool CodeGenPrepare::optimizeMemoryInst(Instruction *MemoryInst, Value *Addr,
   // Now that we determined the addressing expression we want to use and know
   // that we have to sink it into this block.  Check to see if we have already
   // done this for some other load/store instr in this block.  If so, reuse the
-  // computation.
+  // computation.  Before attempting reuse, check if the address is valid as it
+  // may have been erased.
+  auto I = SunkAddrs.find(Addr);
+  if (I != SunkAddrs.end() && I->second && I->second->user_empty())
+    SunkAddrs.erase(I);
+
   Value *&SunkAddr = SunkAddrs[Addr];
   if (SunkAddr) {
     DEBUG(dbgs() << "CGP: Reusing nonlocal addrmode: " << AddrMode << " for "