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llvm-project/llvm/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. llvm-svn: 122378
2010-12-22 07:54:34 +08:00
; 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. llvm-svn: 141177
2011-10-05 22:28:49 +08:00
; 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. llvm-svn: 122378
2010-12-22 07:54:34 +08:00
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. llvm-svn: 141176
2011-10-05 22:17:01 +08:00
}
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. llvm-svn: 141177
2011-10-05 22:28:49 +08:00
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. llvm-svn: 141360
2011-10-07 16:29:06 +08:00
; 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
}