[PATCH] D39841: [CodeGenPrepare] Check that erased sunken address are not reused

[Simon Dardis via Phabricator via llvm-commits]

sdardis created this revision.

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 resolves PR35209.

Thanks to Alexander Richardson for reporting the issue!


Repository:
  rL LLVM

https://reviews.llvm.org/D39841

Files:
  lib/CodeGen/CodeGenPrepare.cpp
  test/Transforms/CodeGenPrepare/pr35209.ll


Index: test/Transforms/CodeGenPrepare/pr35209.ll
===================================================================
--- /dev/null
+++ test/Transforms/CodeGenPrepare/pr35209.ll
@@ -0,0 +1,49 @@
+; RUN: llc -start-before=codegenprepare -stop-after=codegenprepare < %s
+
+; Test that if an address that was sunk from a dominating bb, used in a
+; select that is erased along with its' trivally dead operand, that the
+; sunken address is not reused if the same address computation occurs
+; after the select. Previously, this caused a ICE.
+
+%struct.az = type { i32, %struct.bt* }
+%struct.bt = type { i32 }
+%struct.f = type { %struct.ax, %union.anon }
+%struct.ax = type { %struct.az* }
+%union.anon = type { %struct.bd }
+%struct.bd = type { i64 }
+%struct.bg = type { i32, i32 }
+%struct.ap = type { i32, i32 }
+
+ at ch = common global %struct.f zeroinitializer, align 8
+ at j = common local_unnamed_addr global %struct.az* null, align 8
+ at ck = common local_unnamed_addr global i32 0, align 4
+ at h = common local_unnamed_addr global i32 0, align 4
+ at .str = private unnamed_addr constant [1 x i8] zeroinitializer, align 1
+
+define internal void @probestart() {
+entry:
+  %0 = load %struct.az*, %struct.az** @j, align 8
+  %bw = getelementptr inbounds %struct.az, %struct.az* %0, i64 0, i32 1
+  %1 = load i32, i32* @h, align 4
+  %cond = icmp eq i32 %1, 0
+  br i1 %cond, label %sw.bb, label %cl
+
+sw.bb:                                            ; preds = %entry
+  %call = tail call inreg { i64, i64 } @ba(i32* bitcast (%struct.f* @ch to i32*)) #3
+  br label %cl
+
+cl:                                               ; preds = %sw.bb, %entry
+  %2 = load %struct.bt*, %struct.bt** %bw, align 8
+  %tobool = icmp eq %struct.bt* %2, null
+  %3 = load i32, i32* @ck, align 4
+  %.sink5 = select i1 %tobool, i32* getelementptr (%struct.bg, %struct.bg* bitcast (%union.anon* getelementptr inbounds (%struct.f, %struct.f* @ch, i64 0, i32 1) to %struct.bg*), i64 0, i32 1), i32* getelementptr (%struct.ap, %struct.ap* bitcast (%union.anon* getelementptr inbounds (%struct.f, %struct.f* @ch, i64 0, i32 1) to %struct.ap*), i64 0, i32 1)
+  store i32 %3, i32* %.sink5, align 4
+  store i32 1, i32* bitcast (i64* getelementptr inbounds (%struct.f, %struct.f* @ch, i64 0, i32 1, i32 0, i32 0) to i32*), align 8
+  %4 = load %struct.bt*, %struct.bt** %bw, align 8
+  tail call void (i8*, ...) @a(i8* getelementptr inbounds ([1 x i8], [1 x i8]* @.str, i64 0, i64 0), %struct.bt* %4) #3
+  ret void
+}
+
+declare inreg { i64, i64 } @ba(i32*) local_unnamed_addr #1
+
+declare void @a(i8*, ...) local_unnamed_addr #1
Index: lib/CodeGen/CodeGenPrepare.cpp
===================================================================
--- lib/CodeGen/CodeGenPrepare.cpp
+++ lib/CodeGen/CodeGenPrepare.cpp
@@ -4358,7 +4358,12 @@
   // 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 "


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