LCSSA: Add a workaround for another nasty SCEV cache invalidation issue.

I'm not entirely happy with this solution, but I don't see a smarter way currently.
Fixes PR14214.

llvm-svn: 167112

llvm/lib/Transforms/Utils/LCSSA.cpp

@@ -255,6 +255,11 @@ bool LCSSA::ProcessInstruction(Instruction *Inst,
       if (Loop *L = LI->getLoopFor(ExitBB))
         SE->forgetLoop(L);
   }
+
+  // If we added a PHI, drop the cache to avoid invalidating SCEV caches.
+  // FIXME: This is a big hammer, can we clear the cache more selectively?
+  if (SE && !AddedPHIs.empty())
+    SE->forgetLoop(L);
   
   // Rewrite all uses outside the loop in terms of the new PHIs we just
   // inserted.

llvm/test/Transforms/LoopIdiom/scev-invalidation.ll

@@ -0,0 +1,74 @@
+; RUN: opt -S -indvars -loop-idiom < %s
+; PR14214
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
+target triple = "x86_64-unknown-linux-gnu"
+
+define i32 @quote_arg() nounwind {
+entry:
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.inc, %entry
+  %backslashes.0 = phi i32 [ undef, %entry ], [ %backslashes.2, %for.inc ]
+  %p.0 = phi i8* [ undef, %entry ], [ %incdec.ptr3, %for.inc ]
+  %q.0 = phi i8* [ undef, %entry ], [ %q.2, %for.inc ]
+  %0 = load i8* %p.0, align 1
+  switch i8 %0, label %while.cond.preheader [
+    i8 0, label %for.cond4.preheader
+    i8 92, label %for.inc
+  ]
+
+while.cond.preheader:                             ; preds = %for.cond
+  %tobool210 = icmp eq i32 %backslashes.0, 0
+  br i1 %tobool210, label %for.inc.loopexit, label %while.body.lr.ph
+
+while.body.lr.ph:                                 ; preds = %while.cond.preheader
+  %1 = add i32 %backslashes.0, -1
+  %2 = zext i32 %1 to i64
+  br label %while.body
+
+for.cond4.preheader:                              ; preds = %for.cond
+  %tobool57 = icmp eq i32 %backslashes.0, 0
+  br i1 %tobool57, label %for.end10, label %for.body6.lr.ph
+
+for.body6.lr.ph:                                  ; preds = %for.cond4.preheader
+  br label %for.body6
+
+while.body:                                       ; preds = %while.body.lr.ph, %while.body
+  %q.112 = phi i8* [ %q.0, %while.body.lr.ph ], [ %incdec.ptr, %while.body ]
+  %backslashes.111 = phi i32 [ %backslashes.0, %while.body.lr.ph ], [ %dec, %while.body ]
+  %incdec.ptr = getelementptr inbounds i8* %q.112, i64 1
+  store i8 92, i8* %incdec.ptr, align 1
+  %dec = add nsw i32 %backslashes.111, -1
+  %tobool2 = icmp eq i32 %dec, 0
+  br i1 %tobool2, label %while.cond.for.inc.loopexit_crit_edge, label %while.body
+
+while.cond.for.inc.loopexit_crit_edge:            ; preds = %while.body
+  %scevgep.sum = add i64 %2, 1
+  %scevgep13 = getelementptr i8* %q.0, i64 %scevgep.sum
+  br label %for.inc.loopexit
+
+for.inc.loopexit:                                 ; preds = %while.cond.for.inc.loopexit_crit_edge, %while.cond.preheader
+  %q.1.lcssa = phi i8* [ %scevgep13, %while.cond.for.inc.loopexit_crit_edge ], [ %q.0, %while.cond.preheader ]
+  br label %for.inc
+
+for.inc:                                          ; preds = %for.inc.loopexit, %for.cond
+  %backslashes.2 = phi i32 [ %backslashes.0, %for.cond ], [ 0, %for.inc.loopexit ]
+  %q.2 = phi i8* [ %q.0, %for.cond ], [ %q.1.lcssa, %for.inc.loopexit ]
+  %incdec.ptr3 = getelementptr inbounds i8* %p.0, i64 1
+  br label %for.cond
+
+for.body6:                                        ; preds = %for.body6.lr.ph, %for.body6
+  %q.39 = phi i8* [ %q.0, %for.body6.lr.ph ], [ %incdec.ptr7, %for.body6 ]
+  %backslashes.38 = phi i32 [ %backslashes.0, %for.body6.lr.ph ], [ %dec9, %for.body6 ]
+  %incdec.ptr7 = getelementptr inbounds i8* %q.39, i64 1
+  store i8 92, i8* %incdec.ptr7, align 1
+  %dec9 = add nsw i32 %backslashes.38, -1
+  %tobool5 = icmp eq i32 %dec9, 0
+  br i1 %tobool5, label %for.cond4.for.end10_crit_edge, label %for.body6
+
+for.cond4.for.end10_crit_edge:                    ; preds = %for.body6
+  br label %for.end10
+
+for.end10:                                        ; preds = %for.cond4.for.end10_crit_edge, %for.cond4.preheader
+  ret i32 undef
+}