rdar://12100355 (part 1)

This revision attempts to recognize following population-count pattern:

 while(a) { c++; ... ; a &= a - 1; ... },
  where <c> and <a>could be used multiple times in the loop body.

 TODO: On X8664 and ARM, __buildin_ctpop() are not expanded to a efficent 
instruction sequence, which need to be improved in the following commits.

Reviewed by Nadav, really appreciate!

llvm-svn: 168931

1 files changed, 76 insertions, 0 deletions

diff --git a/llvm/test/Transforms/LoopIdiom/popcnt.ll b/llvm/test/Transforms/LoopIdiom/popcnt.ll
new file mode 100644
index 00000000000..039af8024d3
--- /dev/null
+++ b/llvm/test/Transforms/LoopIdiom/popcnt.ll
@@ -0,0 +1,76 @@
+; RUN: opt -loop-idiom < %s -mtriple=x86_64-apple-darwin -mcpu=corei7 -S | FileCheck %s
+
+;To recognize this pattern:
+;int popcount(unsigned long long a) {
+;    int c = 0;
+;    while (a) {
+;        c++;
+;        a &= a - 1;
+;    }
+;    return c;
+;}
+; 
+; CHECK: entry
+; CHECK: llvm.ctpop.i64
+; CHECK: ret
+define i32 @popcount(i64 %a) nounwind uwtable readnone ssp {
+entry:
+  %tobool3 = icmp eq i64 %a, 0
+  br i1 %tobool3, label %while.end, label %while.body
+
+while.body:                                       ; preds = %entry, %while.body
+  %c.05 = phi i32 [ %inc, %while.body ], [ 0, %entry ]
+  %a.addr.04 = phi i64 [ %and, %while.body ], [ %a, %entry ]
+  %inc = add nsw i32 %c.05, 1
+  %sub = add i64 %a.addr.04, -1
+  %and = and i64 %sub, %a.addr.04
+  %tobool = icmp eq i64 %and, 0
+  br i1 %tobool, label %while.end, label %while.body
+
+while.end:                                        ; preds = %while.body, %entry
+  %c.0.lcssa = phi i32 [ 0, %entry ], [ %inc, %while.body ]
+  ret i32 %c.0.lcssa
+}
+
+; To recognize this pattern:
+;int popcount(unsigned long long a, int mydata1, int mydata2) {
+;    int c = 0;
+;    while (a) {
+;        c++;
+;        a &= a - 1;
+;        mydata1 *= c;
+;        mydata2 *= (int)a;
+;    }
+;    return c + mydata1 + mydata2;
+;}
+; CHECK: entry
+; CHECK: llvm.ctpop.i64
+; CHECK: ret
+define i32 @popcount2(i64 %a, i32 %mydata1, i32 %mydata2) nounwind uwtable readnone ssp {
+entry:
+  %tobool9 = icmp eq i64 %a, 0
+  br i1 %tobool9, label %while.end, label %while.body
+
+while.body:                                       ; preds = %entry, %while.body
+  %c.013 = phi i32 [ %inc, %while.body ], [ 0, %entry ]
+  %mydata2.addr.012 = phi i32 [ %mul1, %while.body ], [ %mydata2, %entry ]
+  %mydata1.addr.011 = phi i32 [ %mul, %while.body ], [ %mydata1, %entry ]
+  %a.addr.010 = phi i64 [ %and, %while.body ], [ %a, %entry ]
+  %inc = add nsw i32 %c.013, 1
+  %sub = add i64 %a.addr.010, -1
+  %and = and i64 %sub, %a.addr.010
+  %mul = mul nsw i32 %inc, %mydata1.addr.011
+  %conv = trunc i64 %and to i32
+  %mul1 = mul nsw i32 %conv, %mydata2.addr.012
+  %tobool = icmp eq i64 %and, 0
+  br i1 %tobool, label %while.end, label %while.body
+
+while.end:                                        ; preds = %while.body, %entry
+  %c.0.lcssa = phi i32 [ 0, %entry ], [ %inc, %while.body ]
+  %mydata2.addr.0.lcssa = phi i32 [ %mydata2, %entry ], [ %mul1, %while.body ]
+  %mydata1.addr.0.lcssa = phi i32 [ %mydata1, %entry ], [ %mul, %while.body ]
+  %add = add i32 %mydata2.addr.0.lcssa, %mydata1.addr.0.lcssa
+  %add2 = add i32 %add, %c.0.lcssa
+  ret i32 %add2
+}
+