[llvm] r296345 - Loop predication expand both sides of the widened condition

[Artur Pilipenko via llvm-commits]

Author: apilipenko
Date: Mon Feb 27 09:44:49 2017
New Revision: 296345

URL: http://llvm.org/viewvc/llvm-project?rev=296345&view=rev
Log:
Loop predication expand both sides of the widened condition

This is a fix for a loop predication bug which resulted in malformed IR generation.

Loop invariant side of the widened condition is not guaranteed to be available in the preheader as is, so we need to expand it as well. See added unsigned_loop_0_to_n_hoist_length test for example.

Reviewed By: sanjoy, mkazantsev

Differential Revision: https://reviews.llvm.org/D30099

Modified:
    llvm/trunk/lib/Transforms/Scalar/LoopPredication.cpp
    llvm/trunk/test/Transforms/LoopPredication/basic.ll

Modified: llvm/trunk/lib/Transforms/Scalar/LoopPredication.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/LoopPredication.cpp?rev=296345&r1=296344&r2=296345&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/LoopPredication.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/LoopPredication.cpp Mon Feb 27 09:44:49 2017
@@ -141,10 +141,9 @@ Optional<Value *> LoopPredication::widen
     std::swap(LHSS, RHSS);
     Pred = ICmpInst::getSwappedPredicate(Pred);
   }
-  if (!SE->isLoopInvariant(RHSS, L))
+  if (!SE->isLoopInvariant(RHSS, L) || !isSafeToExpand(RHSS, *SE))
     return None;
 
-  Value *Bound = RHS;
   const SCEVAddRecExpr *IndexAR = dyn_cast<SCEVAddRecExpr>(LHSS);
   if (!IndexAR || IndexAR->getLoop() != L)
     return None;
@@ -176,9 +175,12 @@ Optional<Value *> LoopPredication::widen
 
   DEBUG(dbgs() << "NewLHSS is loop invariant and safe to expand. Expand!\n");
 
-  Value *NewLHS = Expander.expandCodeFor(NewLHSS, Bound->getType(),
-                                         Preheader->getTerminator());
-  return Builder.CreateICmp(Pred, NewLHS, Bound);
+  Type *Ty = LHS->getType();
+  Instruction *InsertAt = Preheader->getTerminator();
+  assert(Ty == RHS->getType() && "icmp operands have different types?");
+  Value *NewLHS = Expander.expandCodeFor(NewLHSS, Ty, InsertAt);
+  Value *NewRHS = Expander.expandCodeFor(RHSS, Ty, InsertAt);
+  return Builder.CreateICmp(Pred, NewLHS, NewRHS);
 }
 
 bool LoopPredication::widenGuardConditions(IntrinsicInst *Guard,

Modified: llvm/trunk/test/Transforms/LoopPredication/basic.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/LoopPredication/basic.ll?rev=296345&r1=296344&r2=296345&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/LoopPredication/basic.ll (original)
+++ llvm/trunk/test/Transforms/LoopPredication/basic.ll Mon Feb 27 09:44:49 2017
@@ -493,4 +493,79 @@ loop:
 exit:
   %result = phi i32 [ 0, %entry ], [ %loop.acc.next, %loop ]
   ret i32 %result
-}
\ No newline at end of file
+}
+
+define i32 @unsigned_loop_0_to_n_hoist_length(i32* %array, i16 %length.i16, i32 %n) {
+; CHECK-LABEL: @unsigned_loop_0_to_n_hoist_length
+entry:
+  %tmp5 = icmp eq i32 %n, 0
+  br i1 %tmp5, label %exit, label %loop.preheader
+
+loop.preheader:
+; CHECK: loop.preheader:
+; CHECK: [[max_index:[^ ]+]] = add i32 %n, -1
+; CHECK-NEXT: [[length:[^ ]+]] = zext i16 %length.i16 to i32
+; CHECK-NEXT: [[wide_cond:[^ ]+]] = icmp ult i32 [[max_index]], [[length]]
+; CHECK-NEXT: br label %loop
+  br label %loop
+
+loop:
+; CHECK: loop:
+; CHECK: call void (i1, ...) @llvm.experimental.guard(i1 [[wide_cond]], i32 9) [ "deopt"() ]
+  %loop.acc = phi i32 [ %loop.acc.next, %loop ], [ 0, %loop.preheader ]
+  %i = phi i32 [ %i.next, %loop ], [ 0, %loop.preheader ]
+  %length = zext i16 %length.i16 to i32
+  %within.bounds = icmp ult i32 %i, %length
+  call void (i1, ...) @llvm.experimental.guard(i1 %within.bounds, i32 9) [ "deopt"() ]
+
+  %i.i64 = zext i32 %i to i64
+  %array.i.ptr = getelementptr inbounds i32, i32* %array, i64 %i.i64
+  %array.i = load i32, i32* %array.i.ptr, align 4
+  %loop.acc.next = add i32 %loop.acc, %array.i
+
+  %i.next = add nuw i32 %i, 1
+  %continue = icmp ult i32 %i.next, %n
+  br i1 %continue, label %loop, label %exit
+
+exit:
+  %result = phi i32 [ 0, %entry ], [ %loop.acc.next, %loop ]
+  ret i32 %result
+}
+
+define i32 @unsigned_loop_0_to_n_cant_hoist_length(i32* %array, i32 %length, i32 %divider, i32 %n) {
+; CHECK-LABEL: @unsigned_loop_0_to_n_cant_hoist_length
+entry:
+  %tmp5 = icmp eq i32 %n, 0
+  br i1 %tmp5, label %exit, label %loop.preheader
+
+loop.preheader:
+; CHECK: loop.preheader:
+; CHECK-NEXT: br label %loop
+  br label %loop
+
+loop:
+; CHECK: loop:
+; CHECK-NEXT: %loop.acc = phi i32 [ %loop.acc.next, %loop ], [ 0, %loop.preheader ]
+; CHECK-NEXT: %i = phi i32 [ %i.next, %loop ], [ 0, %loop.preheader ]
+; CHECK-NEXT: %length.udiv = udiv i32 %length, %divider
+; CHECK-NEXT: %within.bounds = icmp ult i32 %i, %length.udiv
+; CHECK-NEXT: call void (i1, ...) @llvm.experimental.guard(i1 %within.bounds, i32 9) [ "deopt"() ]
+  %loop.acc = phi i32 [ %loop.acc.next, %loop ], [ 0, %loop.preheader ]
+  %i = phi i32 [ %i.next, %loop ], [ 0, %loop.preheader ]
+  %length.udiv = udiv i32 %length, %divider
+  %within.bounds = icmp ult i32 %i, %length.udiv
+  call void (i1, ...) @llvm.experimental.guard(i1 %within.bounds, i32 9) [ "deopt"() ]
+
+  %i.i64 = zext i32 %i to i64
+  %array.i.ptr = getelementptr inbounds i32, i32* %array, i64 %i.i64
+  %array.i = load i32, i32* %array.i.ptr, align 4
+  %loop.acc.next = add i32 %loop.acc, %array.i
+
+  %i.next = add nuw i32 %i, 1
+  %continue = icmp ult i32 %i.next, %n
+  br i1 %continue, label %loop, label %exit
+
+exit:
+  %result = phi i32 [ 0, %entry ], [ %loop.acc.next, %loop ]
+  ret i32 %result
+}