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llvm-6502/test/Transforms/GVN/condprop.ll

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Give GVN back the ability to perform simple conditional propagation on conditional branch values. I still think that LVI should be handling this, but that capability is some ways off in the future, and this matters for some significant benchmarks. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122378 91177308-0d34-0410-b5e6-96231b3b80d8
2010-12-21 23:54:34 +00:00
; RUN: opt < %s -basicaa -gvn -S | FileCheck %s
@a = external global i32 ; <i32*> [#uses=7]
GVN does simple propagation of conditions: when it sees a conditional branch "br i1 %x, label %if_true, label %if_false" then it replaces "%x" with "true" in places only reachable via the %if_true arm, and with "false" in places only reachable via the %if_false arm. Except that actually it doesn't: if value numbering shows that %y is equal to %x then, yes, %y will be turned into true/false in this way, but any occurrences of %x itself are not transformed. Fix this. What's more, it's often the case that %x is an equality comparison such as "%x = icmp eq %A, 0", in which case every occurrence of %A that is only reachable via the %if_true arm can be replaced with 0. Implement this and a few other variations on this theme. This reduces the number of lines of LLVM IR in "GCC as one big file" by 0.2%. It has a bigger impact on Ada code, typically reducing the number of lines of bitcode by around 0.4% by removing repeated compiler generated checks. Passes the LLVM nightly testsuite and the Ada ACATS testsuite. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@141177 91177308-0d34-0410-b5e6-96231b3b80d8
2011-10-05 14:28:49 +00:00
; CHECK: @test1
define i32 @test1() nounwind {
Give GVN back the ability to perform simple conditional propagation on conditional branch values. I still think that LVI should be handling this, but that capability is some ways off in the future, and this matters for some significant benchmarks. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122378 91177308-0d34-0410-b5e6-96231b3b80d8
2010-12-21 23:54:34 +00:00
entry:
%0 = load i32* @a, align 4
%1 = icmp eq i32 %0, 4
br i1 %1, label %bb, label %bb1
bb: ; preds = %entry
br label %bb8
bb1: ; preds = %entry
%2 = load i32* @a, align 4
%3 = icmp eq i32 %2, 5
br i1 %3, label %bb2, label %bb3
bb2: ; preds = %bb1
br label %bb8
bb3: ; preds = %bb1
%4 = load i32* @a, align 4
%5 = icmp eq i32 %4, 4
; CHECK: br i1 false, label %bb4, label %bb5
br i1 %5, label %bb4, label %bb5
bb4: ; preds = %bb3
%6 = load i32* @a, align 4
%7 = add i32 %6, 5
br label %bb8
bb5: ; preds = %bb3
%8 = load i32* @a, align 4
%9 = icmp eq i32 %8, 5
; CHECK: br i1 false, label %bb6, label %bb7
br i1 %9, label %bb6, label %bb7
bb6: ; preds = %bb5
%10 = load i32* @a, align 4
%11 = add i32 %10, 4
br label %bb8
bb7: ; preds = %bb5
%12 = load i32* @a, align 4
br label %bb8
bb8: ; preds = %bb7, %bb6, %bb4, %bb2, %bb
%.0 = phi i32 [ %12, %bb7 ], [ %11, %bb6 ], [ %7, %bb4 ], [ 4, %bb2 ], [ 5, %bb ]
br label %return
return: ; preds = %bb8
ret i32 %.0
Generalize GVN's conditional propagation logic slightly: it's OK for the false/true destination to have multiple predecessors as long as the extra ones are dominated by the branch destination. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@141176 91177308-0d34-0410-b5e6-96231b3b80d8
2011-10-05 14:17:01 +00:00
}
GVN does simple propagation of conditions: when it sees a conditional branch "br i1 %x, label %if_true, label %if_false" then it replaces "%x" with "true" in places only reachable via the %if_true arm, and with "false" in places only reachable via the %if_false arm. Except that actually it doesn't: if value numbering shows that %y is equal to %x then, yes, %y will be turned into true/false in this way, but any occurrences of %x itself are not transformed. Fix this. What's more, it's often the case that %x is an equality comparison such as "%x = icmp eq %A, 0", in which case every occurrence of %A that is only reachable via the %if_true arm can be replaced with 0. Implement this and a few other variations on this theme. This reduces the number of lines of LLVM IR in "GCC as one big file" by 0.2%. It has a bigger impact on Ada code, typically reducing the number of lines of bitcode by around 0.4% by removing repeated compiler generated checks. Passes the LLVM nightly testsuite and the Ada ACATS testsuite. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@141177 91177308-0d34-0410-b5e6-96231b3b80d8
2011-10-05 14:28:49 +00:00
declare void @foo(i1)
declare void @bar(i32)
; CHECK: @test3
define void @test3(i32 %x, i32 %y) {
%xz = icmp eq i32 %x, 0
%yz = icmp eq i32 %y, 0
%z = and i1 %xz, %yz
br i1 %z, label %both_zero, label %nope
both_zero:
call void @foo(i1 %xz)
; CHECK: call void @foo(i1 true)
call void @foo(i1 %yz)
; CHECK: call void @foo(i1 true)
call void @bar(i32 %x)
; CHECK: call void @bar(i32 0)
call void @bar(i32 %y)
; CHECK: call void @bar(i32 0)
ret void
nope:
call void @foo(i1 %z)
; CHECK: call void @foo(i1 false)
ret void
}
Teach GVN to also propagate switch cases. For example, in this code switch (n) { case 27: do_something(x); ... } the call do_something(x) will be replaced with do_something(27). In gcc-as-one-big-file this results in the removal of about 500 lines of bitcode (about 0.02%), so has about 1/10 of the effect of propagating branch conditions. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@141360 91177308-0d34-0410-b5e6-96231b3b80d8
2011-10-07 08:29:06 +00:00
; CHECK: @test4
define void @test4(i1 %b, i32 %x) {
br i1 %b, label %sw, label %case3
sw:
switch i32 %x, label %default [
i32 0, label %case0
i32 1, label %case1
i32 2, label %case0
i32 3, label %case3
i32 4, label %default
]
default:
; CHECK: default:
call void @bar(i32 %x)
; CHECK: call void @bar(i32 %x)
ret void
case0:
; CHECK: case0:
call void @bar(i32 %x)
; CHECK: call void @bar(i32 %x)
ret void
case1:
; CHECK: case1:
call void @bar(i32 %x)
; CHECK: call void @bar(i32 1)
ret void
case3:
; CHECK: case3:
call void @bar(i32 %x)
; CHECK: call void @bar(i32 %x)
ret void
}
When performing a conditional branch depending on the value of a comparison %cmp (eg: A==B) we already replace %cmp with "true" under the true edge, and with "false" under the false edge. This change enhances this to replace the negated compare (A!=B) with "false" under the true edge and "true" under the false edge. Reported to improve perlbench results by 1%. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@151517 91177308-0d34-0410-b5e6-96231b3b80d8
2012-02-27 08:14:30 +00:00
; CHECK: @test5
define i1 @test5(i32 %x, i32 %y) {
%cmp = icmp eq i32 %x, %y
br i1 %cmp, label %same, label %different
same:
%cmp2 = icmp ne i32 %x, %y
; CHECK: ret i1 false
ret i1 %cmp2
different:
%cmp3 = icmp eq i32 %x, %y
; CHECK: ret i1 false
ret i1 %cmp3
}
; CHECK: @test6
define i1 @test6(i32 %x, i32 %y) {
%cmp2 = icmp ne i32 %x, %y
%cmp = icmp eq i32 %x, %y
%cmp3 = icmp eq i32 %x, %y
br i1 %cmp, label %same, label %different
same:
; CHECK: ret i1 false
ret i1 %cmp2
different:
; CHECK: ret i1 false
ret i1 %cmp3
}
; CHECK: @test7
define i1 @test7(i32 %x, i32 %y) {
%cmp = icmp sgt i32 %x, %y
br i1 %cmp, label %same, label %different
same:
%cmp2 = icmp sle i32 %x, %y
; CHECK: ret i1 false
ret i1 %cmp2
different:
%cmp3 = icmp sgt i32 %x, %y
; CHECK: ret i1 false
ret i1 %cmp3
}
; CHECK: @test8
define i1 @test8(i32 %x, i32 %y) {
%cmp2 = icmp sle i32 %x, %y
%cmp = icmp sgt i32 %x, %y
%cmp3 = icmp sgt i32 %x, %y
br i1 %cmp, label %same, label %different
same:
; CHECK: ret i1 false
ret i1 %cmp2
different:
; CHECK: ret i1 false
ret i1 %cmp3
}
Have GVN also do condition propagation when the right-hand side is not a constant. This fixes PR1768. git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@151713 91177308-0d34-0410-b5e6-96231b3b80d8
2012-02-29 11:12:03 +00:00
; PR1768
; CHECK: @test9
define i32 @test9(i32 %i, i32 %j) {
%cmp = icmp eq i32 %i, %j
br i1 %cmp, label %cond_true, label %ret
cond_true:
%diff = sub i32 %i, %j
ret i32 %diff
; CHECK: ret i32 0
ret:
ret i32 5
; CHECK: ret i32 5
}
; PR1768
; CHECK: @test10
define i32 @test10(i32 %j, i32 %i) {
%cmp = icmp eq i32 %i, %j
br i1 %cmp, label %cond_true, label %ret
cond_true:
%diff = sub i32 %i, %j
ret i32 %diff
; CHECK: ret i32 0
ret:
ret i32 5
; CHECK: ret i32 5
}
declare i32 @yogibar()
; CHECK: @test11
define i32 @test11(i32 %x) {
%v0 = call i32 @yogibar()
%v1 = call i32 @yogibar()
%cmp = icmp eq i32 %v0, %v1
br i1 %cmp, label %cond_true, label %next
cond_true:
ret i32 %v1
; CHECK: ret i32 %v0
next:
%cmp2 = icmp eq i32 %x, %v0
br i1 %cmp2, label %cond_true2, label %next2
cond_true2:
ret i32 %v0
; CHECK: ret i32 %x
next2:
ret i32 0
}
Nick pointed out on IRC that GVN's propagateEquality wasn't propagating equalities into phi node operands for which the equality is known to hold in the incoming basic block. That's because replaceAllDominatedUsesWith wasn't handling phi nodes correctly in general (that this didn't give wrong results was just luck: the specific way GVN uses replaceAllDominatedUsesWith precluded wrong changes to phi nodes). git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@152006 91177308-0d34-0410-b5e6-96231b3b80d8
2012-03-04 13:25:19 +00:00
; CHECK: @test12
define i32 @test12(i32 %x) {
%cmp = icmp eq i32 %x, 0
br i1 %cmp, label %cond_true, label %cond_false
cond_true:
br label %ret
cond_false:
br label %ret
ret:
%res = phi i32 [ %x, %cond_true ], [ %x, %cond_false ]
; CHECK: %res = phi i32 [ 0, %cond_true ], [ %x, %cond_false ]
ret i32 %res
}
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