From e5ca494ae6fdf502bbff051a0d468ca7aa610639 Mon Sep 17 00:00:00 2001 From: Chandler Carruth Date: Sun, 9 Jan 2011 09:58:36 +0000 Subject: Another missed optimization of trivial vector code. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@123112 91177308-0d34-0410-b5e6-96231b3b80d8 --- lib/Target/README.txt | 33 +++++++++++++++++++++++++++++++++ 1 file changed, 33 insertions(+) (limited to 'lib/Target/README.txt') diff --git a/lib/Target/README.txt b/lib/Target/README.txt index 719f2faeff..ff392f491d 100644 --- a/lib/Target/README.txt +++ b/lib/Target/README.txt @@ -2193,3 +2193,36 @@ is the fact that all three null stores in %entry are dead, but not eliminated. Also surprising is that %conv isn't simplified to 0 in %....exit.thread.i.i. //===---------------------------------------------------------------------===// + +clang -O3 -fno-exceptions currently compiles this code: + +void f(int N) { + std::vector v(N); + g(v); +} + +into almost the same as the previous note, but replace its final BB with: + +for.body.lr.ph: ; preds = %cond.true.i.i.i.i + %mul.i.i.i.i.i = shl i64 %conv, 2 + %call3.i.i.i.i.i = call noalias i8* @_Znwm(i64 %mul.i.i.i.i.i) nounwind + %0 = bitcast i8* %call3.i.i.i.i.i to i32* + store i32* %0, i32** %v8.sub, align 8, !tbaa !0 + %add.ptr.i.i.i = getelementptr inbounds i32* %0, i64 %conv + store i32* %add.ptr.i.i.i, i32** %tmp4.i.i.i.i.i, align 8, !tbaa !0 + call void @llvm.memset.p0i8.i64(i8* %call3.i.i.i.i.i, i8 0, i64 %mul.i.i.i.i.i, i32 4, i1 false) + store i32* %add.ptr.i.i.i, i32** %tmp3.i.i.i.i.i, align 8, !tbaa !0 + %tmp18 = add i32 %N, -1 + %tmp19 = zext i32 %tmp18 to i64 + %tmp20 = shl i64 %tmp19, 2 + %tmp21 = add i64 %tmp20, 4 + call void @llvm.memset.p0i8.i64(i8* %call3.i.i.i.i.i, i8 0, i64 %tmp21, i32 4, i1 false) + br label %for.end + +First off, why (((zext %N - 1) << 2) + 4) instead of the ((sext %N) << 2) done +previously? (or better yet, re-use that one?) + +Then, the really painful one is the second memset, of the same memory, to the +same value. + +//===---------------------------------------------------------------------===// -- cgit v1.2.3