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llvm-project/llvm/test/Transforms/CorrelatedValuePropagation/select.ll

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CVP: Improve handling of Selects used as incoming PHI values Summary: If the branch that leads to the PHI node and the Select instruction depend on correlated conditions, we might be able to directly use the corresponding value from the Select instruction as the incoming value for the PHI node, allowing later removal of the select instruction. Subscribers: llvm-commits Differential Revision: http://reviews.llvm.org/D9051 llvm-svn: 237201
2015-05-13 06:31:47 +08:00
; RUN: opt < %s -correlated-propagation -S | FileCheck %s
; CHECK-LABEL: @simple(
define i8 @simple(i1) {
entry:
%s = select i1 %0, i8 0, i8 1
br i1 %0, label %then, label %else
then:
; CHECK: ret i8 0
%a = phi i8 [ %s, %entry ]
ret i8 %a
else:
; CHECK: ret i8 1
%b = phi i8 [ %s, %entry ]
ret i8 %b
}
; CHECK-LABEL: @loop(
define void @loop(i32) {
entry:
br label %loop
loop:
%idx = phi i32 [ %0, %entry ], [ %sel, %loop ]
; CHECK: %idx = phi i32 [ %0, %entry ], [ %2, %loop ]
%1 = icmp eq i32 %idx, 0
%2 = add i32 %idx, -1
%sel = select i1 %1, i32 0, i32 %2
br i1 %1, label %out, label %loop
out:
ret void
}
; CHECK-LABEL: @not_correlated(
define i8 @not_correlated(i1, i1) {
entry:
%s = select i1 %0, i8 0, i8 1
br i1 %1, label %then, label %else
then:
; CHECK: ret i8 %s
%a = phi i8 [ %s, %entry ]
ret i8 %a
else:
; CHECK: ret i8 %s
%b = phi i8 [ %s, %entry ]
ret i8 %b
}
[CVP] Don't assume Constants of type i1 can be known to be true or false CVP wants to analyze the condition operand of a select along an edge. It succeeds in getting back a Constant but not a ConstantInt. Instead, it gets a ConstantExpr. It then assumes that the Constant must be equal to false because it isn't equal to true. Instead, perform an additional comparison. This fixes PR23752. llvm-svn: 239217
2015-06-06 12:56:51 +08:00
@c = global i32 0, align 4
@b = global i32 0, align 4
; CHECK-LABEL: @PR23752(
define i32 @PR23752() {
entry:
br label %for.body
for.body:
%phi = phi i32 [ 0, %entry ], [ %sel, %for.body ]
%sel = select i1 icmp sgt (i32* @b, i32* @c), i32 %phi, i32 1
%cmp = icmp ne i32 %sel, 1
br i1 %cmp, label %for.body, label %if.end
; CHECK: %[[sel:.*]] = select i1 icmp sgt (i32* @b, i32* @c), i32 0, i32 1
; CHECK-NEXT: %[[cmp:.*]] = icmp ne i32 %[[sel]], 1
; CHECK-NEXT: br i1 %[[cmp]]
if.end:
ret i32 %sel
[CVP] Fold return values if possible In my previous change to CVP (251606), I made CVP much more aggressive about trying to constant fold comparisons. This patch is a reversal in direction. Rather than being agressive about every compare, we restore the non-block local restriction for most, and then try hard for compares feeding returns. The motivation for this is two fold: * The more I thought about it, the less comfortable I got with the possible compile time impact of the other approach. There have been no reported issues, but after talking to a couple of folks, I've come to the conclusion the time probably isn't justified. * It turns out we need to know the context to leverage the full power of LVI. In particular, asking about something at the end of it's block (the use of a compare in a return) will frequently get more precise results than something in the middle of a block. This is an implementation detail, but it's also hard to get around since mid-block queries have to reason about possible throwing instructions and don't get to use most of LVI's block focused infrastructure. This will become particular important when combined with http://reviews.llvm.org/D14263. Differential Revision: http://reviews.llvm.org/D14271 llvm-svn: 252032
2015-11-04 09:43:54 +08:00
; CHECK: ret i32 1
[CVP] Don't assume Constants of type i1 can be known to be true or false CVP wants to analyze the condition operand of a select along an edge. It succeeds in getting back a Constant but not a ConstantInt. Instead, it gets a ConstantExpr. It then assumes that the Constant must be equal to false because it isn't equal to true. Instead, perform an additional comparison. This fixes PR23752. llvm-svn: 239217
2015-06-06 12:56:51 +08:00
}
[LVI] Add select handling Teach LVI to handle select instructions in the exact same way it handles PHI nodes. This is useful since various parts of the optimizer convert PHI nodes into selects and we don't want these transformations to cause inferior optimization. Note that this patch does nothing to exploit the implied constraint on the inputs represented by the select condition itself. That will be a later patch and is blocked on http://reviews.llvm.org/D14476 llvm-svn: 259429
2016-02-02 06:57:53 +08:00
define i1 @test1(i32* %p, i1 %unknown) {
; CHECK-LABEL: @test1
%pval = load i32, i32* %p
%cmp1 = icmp slt i32 %pval, 255
br i1 %cmp1, label %next, label %exit
next:
%min = select i1 %unknown, i32 %pval, i32 5
;; TODO: This pointless branch shouldn't be neccessary
br label %next2
next2:
; CHECK-LABEL: next2:
; CHECK: ret i1 false
%res = icmp eq i32 %min, 255
ret i1 %res
exit:
; CHECK-LABEL: exit:
; CHECK: ret i1 true
ret i1 true
}
; Check that we take a conservative meet
define i1 @test2(i32* %p, i32 %qval, i1 %unknown) {
; CHECK-LABEL: test2
%pval = load i32, i32* %p
%cmp1 = icmp slt i32 %pval, 255
br i1 %cmp1, label %next, label %exit
next:
%min = select i1 %unknown, i32 %pval, i32 %qval
;; TODO: This pointless branch shouldn't be neccessary
br label %next2
next2:
; CHECK-LABEL: next2
; CHECK: ret i1 %res
%res = icmp eq i32 %min, 255
ret i1 %res
exit:
; CHECK-LABEL: exit:
; CHECK: ret i1 true
ret i1 true
}
; Same as @test2, but for the opposite select input
define i1 @test3(i32* %p, i32 %qval, i1 %unknown) {
; CHECK-LABEL: test3
%pval = load i32, i32* %p
%cmp1 = icmp slt i32 %pval, 255
br i1 %cmp1, label %next, label %exit
next:
%min = select i1 %unknown, i32 %qval, i32 %pval
;; TODO: This pointless branch shouldn't be neccessary
br label %next2
next2:
; CHECK-LABEL: next2
; CHECK: ret i1 %res
%res = icmp eq i32 %min, 255
ret i1 %res
exit:
; CHECK-LABEL: exit:
; CHECK: ret i1 true
ret i1 true
}
[LVI] Missing test case from 259432 llvm-svn: 259437
2016-02-02 07:44:38 +08:00
; Conflicting constants (i.e. isOverdefined result)
; NOTE: Using doubles in this version is a bit of a hack. This
; is to get around the fact that all integers (including constants
; and non-constants) are actually represented as constant-ranges.
define i1 @test4(i32* %p, i32 %qval, i1 %unknown) {
; CHECK-LABEL: test4
%pval = load i32, i32* %p
%cmp1 = icmp slt i32 %pval, 255
br i1 %cmp1, label %next, label %exit
next:
%min = select i1 %unknown, double 1.0, double 0.0
;; TODO: This pointless branch shouldn't be neccessary
br label %next2
next2:
; CHECK-LABEL: next2
; CHECK: ret i1 %res
%res = fcmp oeq double %min, 300.0
ret i1 %res
exit:
; CHECK-LABEL: exit:
; CHECK: ret i1 true
ret i1 true
}
[LVI] Improve select handling to use condition This patches teaches LVI to recognize clamp idioms (e.g. select(a > 5, a, 5) will always produce something greater than 5. The tests end up being somewhat simplistic because trying to exercise the case I actually care about (a loop with a range check on a clamped secondary induction variable) ends up tripping across a couple of other imprecisions in the analysis. Ah, the joys of LVI... Differential Revision: http://reviews.llvm.org/D16827 llvm-svn: 260627
2016-02-12 08:09:18 +08:00
;; Using the condition to clamp the result
;;
define i1 @test5(i32* %p, i1 %unknown) {
; CHECK-LABEL: @test5
%pval = load i32, i32* %p
%cmp1 = icmp slt i32 %pval, 255
br i1 %cmp1, label %next, label %exit
next:
%cond = icmp sgt i32 %pval, 0
%min = select i1 %cond, i32 %pval, i32 5
;; TODO: This pointless branch shouldn't be neccessary
br label %next2
next2:
; CHECK-LABEL: next2:
; CHECK: ret i1 false
%res = icmp eq i32 %min, -1
ret i1 %res
exit:
; CHECK-LABEL: exit:
; CHECK: ret i1 true
ret i1 true
}
define i1 @test6(i32* %p, i1 %unknown) {
; CHECK-LABEL: @test6
%pval = load i32, i32* %p
%cmp1 = icmp ult i32 %pval, 255
br i1 %cmp1, label %next, label %exit
next:
%cond = icmp ne i32 %pval, 254
%sel = select i1 %cond, i32 %pval, i32 1
;; TODO: This pointless branch shouldn't be neccessary
br label %next2
next2:
; CHECK-LABEL: next2:
; CHECK: ret i1 true
%res = icmp slt i32 %sel, 254
ret i1 %res
exit:
; CHECK-LABEL: exit:
; CHECK: ret i1 true
ret i1 true
}