[SimplifyCFG] Hoist implying condition #155986
Description
https://alive2.llvm.org/ce/z/Dj_5qY
define i32 @src(ptr %contents.0, i64 %contents.1) {
start:
%cmp1 = icmp ugt i64 %contents.1, 7
br i1 %cmp1, label %if, label %exit
if:
%load = load i64, ptr %contents.0
%cmp2 = icmp eq i64 %load, 123
%cmp3 = icmp eq i64 %contents.1, 16
%and = and i1 %cmp2, %cmp3
br i1 %and, label %if2, label %exit
if2:
ret i32 1
exit:
ret i32 0
}
define i32 @tgt(ptr %contents.0, i64 %contents.1) {
start:
%cmp1 = icmp eq i64 %contents.1, 16
br i1 %cmp1, label %if, label %exit
if:
%load = load i64, ptr %contents.0
%cmp2 = icmp eq i64 %load, 123
%cmp3 = icmp eq i64 %contents.1, 16
%and = and i1 %cmp2, true
br i1 %and, label %if2, label %exit
if2:
ret i32 1
exit:
ret i32 0
}In this example, %if2 is taken if %cmp1, %cmp2 and %cmp3 are all true, otherwise %exit is taken. However, %cmp3 implies %cmp1. So we can check %cmp3 first. This means that the %if block is not executed anymore in more cases, so it's only possible if it is side-effect free.