From 1bc7315c022b327a496366a78eb31ba446c699bd Mon Sep 17 00:00:00 2001 From: Shuxin Yang Date: Thu, 19 Sep 2013 17:22:51 +0000 Subject: GVN proceeds in the presence of dead code. This is how it ignores the dead code: 1) When a dead branch target, say block B, is identified, all the blocks dominated by B is dead as well. 2) The PHIs of those blocks in dominance-frontier(B) is updated such that the operands corresponding to dead predecessors are replaced by "UndefVal". Using lattice's jargon, the "UndefVal" is the "Top" in essence. Phi node like this "phi(v1 bb1, undef xx)" will be optimized into "v1" if v1 is constant, or v1 is an instruction which dominate this PHI node. 3) When analyzing the availability of a load L, all dead mem-ops which L depends on disguise as a load which evaluate exactly same value as L. 4) The dead mem-ops will be materialized as "UndefVal" during code motion. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191017 91177308-0d34-0410-b5e6-96231b3b80d8 --- test/Transforms/GVN/local-pre.ll | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) (limited to 'test/Transforms/GVN/local-pre.ll') diff --git a/test/Transforms/GVN/local-pre.ll b/test/Transforms/GVN/local-pre.ll index 1d0dadfbe0..2c92699dca 100644 --- a/test/Transforms/GVN/local-pre.ll +++ b/test/Transforms/GVN/local-pre.ll @@ -1,9 +1,9 @@ ; RUN: opt < %s -gvn -enable-pre -S | grep "b.pre" -define i32 @main(i32 %p) { +define i32 @main(i32 %p, i32 %q) { block1: - - br i1 true, label %block2, label %block3 + %cmp = icmp eq i32 %p, %q + br i1 %cmp, label %block2, label %block3 block2: %a = add i32 %p, 1 -- cgit v1.2.3