Adding IV chain generation to LSR.

After collecting chains, check if any should be materialized. If so,
hide the chained IV users from the LSR solver. LSR will only solve for
the head of the chain. GenerateIVChains will then materialize the
chained IV users by computing the IV relative to its previous value in
the chain.

In theory, chained IV users could be exposed to LSR's solver. This
would be considerably complicated to implement and I'm not aware of a
case where we need it. In practice it's more important to
intelligently prune the search space of nontrivial loops before
running the solver, otherwise the solver is often forced to prune the
most optimal solutions. Hiding the chained users does this well, so
that LSR is more likely to find the best IV for the chain as a whole.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@147801 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 96 insertions, 0 deletions

diff --git a/test/Transforms/LoopStrengthReduce/X86/ivchain-stress-X86.ll b/test/Transforms/LoopStrengthReduce/X86/ivchain-stress-X86.ll
new file mode 100644
index 0000000..d8e0aa9
--- /dev/null
+++ b/test/Transforms/LoopStrengthReduce/X86/ivchain-stress-X86.ll
@@ -0,0 +1,96 @@
+; REQUIRES: asserts
+; RUN: llc < %s -O3 -march=x86-64 -mcpu=core2 -stress-ivchain | FileCheck %s -check-prefix=X64
+; RUN: llc < %s -O3 -march=x86 -mcpu=core2 -stress-ivchain | FileCheck %s -check-prefix=X32
+
+; @sharedidx is an unrolled variant of this loop:
+;  for (unsigned long i = 0; i < len; i += s) {
+;    c[i] = a[i] + b[i];
+;  }
+; where 's' cannot be folded into the addressing mode.
+;
+; This is not quite profitable to chain. But with -stress-ivchain, we
+; can form three address chains in place of the shared induction
+; variable.
+
+; X64: sharedidx:
+; X64: %for.body.preheader
+; X64-NOT: leal ({{.*}},4)
+; X64: %for.body.1
+
+; X32: sharedidx:
+; X32: %for.body.2
+; X32: add
+; X32: add
+; X32: add
+; X32: add
+; X32: add
+; X32: %for.body.3
+define void @sharedidx(i8* nocapture %a, i8* nocapture %b, i8* nocapture %c, i32 %s, i32 %len) nounwind ssp {
+entry:
+  %cmp8 = icmp eq i32 %len, 0
+  br i1 %cmp8, label %for.end, label %for.body
+
+for.body:                                         ; preds = %entry, %for.body.3
+  %i.09 = phi i32 [ %add5.3, %for.body.3 ], [ 0, %entry ]
+  %arrayidx = getelementptr inbounds i8* %a, i32 %i.09
+  %0 = load i8* %arrayidx, align 1
+  %conv6 = zext i8 %0 to i32
+  %arrayidx1 = getelementptr inbounds i8* %b, i32 %i.09
+  %1 = load i8* %arrayidx1, align 1
+  %conv27 = zext i8 %1 to i32
+  %add = add nsw i32 %conv27, %conv6
+  %conv3 = trunc i32 %add to i8
+  %arrayidx4 = getelementptr inbounds i8* %c, i32 %i.09
+  store i8 %conv3, i8* %arrayidx4, align 1
+  %add5 = add i32 %i.09, %s
+  %cmp = icmp ult i32 %add5, %len
+  br i1 %cmp, label %for.body.1, label %for.end
+
+for.end:                                          ; preds = %for.body, %for.body.1, %for.body.2, %for.body.3, %entry
+  ret void
+
+for.body.1:                                       ; preds = %for.body
+  %arrayidx.1 = getelementptr inbounds i8* %a, i32 %add5
+  %2 = load i8* %arrayidx.1, align 1
+  %conv6.1 = zext i8 %2 to i32
+  %arrayidx1.1 = getelementptr inbounds i8* %b, i32 %add5
+  %3 = load i8* %arrayidx1.1, align 1
+  %conv27.1 = zext i8 %3 to i32
+  %add.1 = add nsw i32 %conv27.1, %conv6.1
+  %conv3.1 = trunc i32 %add.1 to i8
+  %arrayidx4.1 = getelementptr inbounds i8* %c, i32 %add5
+  store i8 %conv3.1, i8* %arrayidx4.1, align 1
+  %add5.1 = add i32 %add5, %s
+  %cmp.1 = icmp ult i32 %add5.1, %len
+  br i1 %cmp.1, label %for.body.2, label %for.end
+
+for.body.2:                                       ; preds = %for.body.1
+  %arrayidx.2 = getelementptr inbounds i8* %a, i32 %add5.1
+  %4 = load i8* %arrayidx.2, align 1
+  %conv6.2 = zext i8 %4 to i32
+  %arrayidx1.2 = getelementptr inbounds i8* %b, i32 %add5.1
+  %5 = load i8* %arrayidx1.2, align 1
+  %conv27.2 = zext i8 %5 to i32
+  %add.2 = add nsw i32 %conv27.2, %conv6.2
+  %conv3.2 = trunc i32 %add.2 to i8
+  %arrayidx4.2 = getelementptr inbounds i8* %c, i32 %add5.1
+  store i8 %conv3.2, i8* %arrayidx4.2, align 1
+  %add5.2 = add i32 %add5.1, %s
+  %cmp.2 = icmp ult i32 %add5.2, %len
+  br i1 %cmp.2, label %for.body.3, label %for.end
+
+for.body.3:                                       ; preds = %for.body.2
+  %arrayidx.3 = getelementptr inbounds i8* %a, i32 %add5.2
+  %6 = load i8* %arrayidx.3, align 1
+  %conv6.3 = zext i8 %6 to i32
+  %arrayidx1.3 = getelementptr inbounds i8* %b, i32 %add5.2
+  %7 = load i8* %arrayidx1.3, align 1
+  %conv27.3 = zext i8 %7 to i32
+  %add.3 = add nsw i32 %conv27.3, %conv6.3
+  %conv3.3 = trunc i32 %add.3 to i8
+  %arrayidx4.3 = getelementptr inbounds i8* %c, i32 %add5.2
+  store i8 %conv3.3, i8* %arrayidx4.3, align 1
+  %add5.3 = add i32 %add5.2, %s
+  %cmp.3 = icmp ult i32 %add5.3, %len
+  br i1 %cmp.3, label %for.body, label %for.end
+}