[llvm] Reland [SimplifyCFG] Delete the unnecessary range check for small mask operation (PR #70542)
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Wed Nov 1 02:55:02 PDT 2023
https://github.com/vfdff updated https://github.com/llvm/llvm-project/pull/70542
>From cb3f04c4e5fb4dfbdd24aaf0a43b7362503db14c Mon Sep 17 00:00:00 2001
From: zhongyunde 00443407 <zhongyunde at huawei.com>
Date: Fri, 1 Sep 2023 23:05:45 -0400
Subject: [PATCH 1/2] [SimplifyCFG] Delete the unnecessary range check for
small mask operation
When the small mask value little than 64, we can eliminate the checking
for upper limit of the range by enlarge the lookup table size to the maximum
index value. (Then the final table size grows to the next pow2 value)
```
bool f(unsigned x) {
switch (x % 8) {
case 0: return 1;
case 1: return 0;
case 2: return 0;
case 3: return 1;
case 4: return 1;
case 5: return 0;
case 6: return 1;
// This would remove the range check: case 7: return 0;
}
return 0;
}
```
Use WouldFitInRegister instead of fitsInLegalInteger to support
more result type beside bool.
Fixes https://github.com/llvm/llvm-project/issues/65120
---
llvm/lib/Transforms/Utils/SimplifyCFG.cpp | 22 +++++++++++++++--
.../Transforms/SimplifyCFG/switch_mask.ll | 24 ++++++++-----------
2 files changed, 30 insertions(+), 16 deletions(-)
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 68b5b1a78a3460e..18187bcdedf0982 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -6598,9 +6598,8 @@ static bool SwitchToLookupTable(SwitchInst *SI, IRBuilder<> &Builder,
// If the default destination is unreachable, or if the lookup table covers
// all values of the conditional variable, branch directly to the lookup table
// BB. Otherwise, check that the condition is within the case range.
- const bool DefaultIsReachable =
+ bool DefaultIsReachable =
!isa<UnreachableInst>(SI->getDefaultDest()->getFirstNonPHIOrDbg());
- const bool GeneratingCoveredLookupTable = (MaxTableSize == TableSize);
// Create the BB that does the lookups.
Module &Mod = *CommonDest->getParent()->getParent();
@@ -6631,6 +6630,25 @@ static bool SwitchToLookupTable(SwitchInst *SI, IRBuilder<> &Builder,
BranchInst *RangeCheckBranch = nullptr;
+ // Grow the table to cover all possible index values to avoid the range check.
+ if (UseSwitchConditionAsTableIndex) {
+ ConstantRange CR = computeConstantRange(TableIndex, /* ForSigned */ false);
+ // Grow the table shouldn't have any size impact by checking
+ // WouldFitInRegister.
+ // TODO: Consider growing the table also when it doesn't fit in a register
+ // if no optsize is specified.
+ if (all_of(ResultTypes, [&](const auto &KV) {
+ return SwitchLookupTable::WouldFitInRegister(
+ DL, CR.getUpper().getLimitedValue(), KV.second /* ResultType */);
+ })) {
+ // The default branch is unreachable when we enlarge the lookup table.
+ // Adjust DefaultIsReachable to reuse code path.
+ TableSize = CR.getUpper().getZExtValue();
+ DefaultIsReachable = false;
+ }
+ }
+
+ const bool GeneratingCoveredLookupTable = (MaxTableSize == TableSize);
if (!DefaultIsReachable || GeneratingCoveredLookupTable) {
Builder.CreateBr(LookupBB);
if (DTU)
diff --git a/llvm/test/Transforms/SimplifyCFG/switch_mask.ll b/llvm/test/Transforms/SimplifyCFG/switch_mask.ll
index 8c97a0660d07074..123519bc6921147 100644
--- a/llvm/test/Transforms/SimplifyCFG/switch_mask.ll
+++ b/llvm/test/Transforms/SimplifyCFG/switch_mask.ll
@@ -8,13 +8,11 @@ define i1 @switch_lookup_with_small_i1(i64 %x) {
; CHECK-LABEL: @switch_lookup_with_small_i1(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[AND:%.*]] = and i64 [[X:%.*]], 15
-; CHECK-NEXT: [[TMP0:%.*]] = icmp ult i64 [[AND]], 11
-; CHECK-NEXT: [[SWITCH_CAST:%.*]] = trunc i64 [[AND]] to i11
-; CHECK-NEXT: [[SWITCH_SHIFTAMT:%.*]] = mul nuw nsw i11 [[SWITCH_CAST]], 1
-; CHECK-NEXT: [[SWITCH_DOWNSHIFT:%.*]] = lshr i11 -1018, [[SWITCH_SHIFTAMT]]
-; CHECK-NEXT: [[SWITCH_MASKED:%.*]] = trunc i11 [[SWITCH_DOWNSHIFT]] to i1
-; CHECK-NEXT: [[TMP1:%.*]] = select i1 [[TMP0]], i1 [[SWITCH_MASKED]], i1 false
-; CHECK-NEXT: ret i1 [[TMP1]]
+; CHECK-NEXT: [[SWITCH_CAST:%.*]] = trunc i64 [[AND]] to i16
+; CHECK-NEXT: [[SWITCH_SHIFTAMT:%.*]] = mul nuw nsw i16 [[SWITCH_CAST]], 1
+; CHECK-NEXT: [[SWITCH_DOWNSHIFT:%.*]] = lshr i16 1030, [[SWITCH_SHIFTAMT]]
+; CHECK-NEXT: [[SWITCH_MASKED:%.*]] = trunc i16 [[SWITCH_DOWNSHIFT]] to i1
+; CHECK-NEXT: ret i1 [[SWITCH_MASKED]]
;
entry:
%and = and i64 %x, 15
@@ -37,13 +35,11 @@ define i8 @switch_lookup_with_small_i8(i64 %x) {
; CHECK-LABEL: @switch_lookup_with_small_i8(
; CHECK-NEXT: entry:
; CHECK-NEXT: [[REM:%.*]] = urem i64 [[X:%.*]], 5
-; CHECK-NEXT: [[TMP0:%.*]] = icmp ult i64 [[REM]], 3
-; CHECK-NEXT: [[SWITCH_CAST:%.*]] = trunc i64 [[REM]] to i24
-; CHECK-NEXT: [[SWITCH_SHIFTAMT:%.*]] = mul nuw nsw i24 [[SWITCH_CAST]], 8
-; CHECK-NEXT: [[SWITCH_DOWNSHIFT:%.*]] = lshr i24 460303, [[SWITCH_SHIFTAMT]]
-; CHECK-NEXT: [[SWITCH_MASKED:%.*]] = trunc i24 [[SWITCH_DOWNSHIFT]] to i8
-; CHECK-NEXT: [[TMP1:%.*]] = select i1 [[TMP0]], i8 [[SWITCH_MASKED]], i8 0
-; CHECK-NEXT: ret i8 [[TMP1]]
+; CHECK-NEXT: [[SWITCH_CAST:%.*]] = trunc i64 [[REM]] to i40
+; CHECK-NEXT: [[SWITCH_SHIFTAMT:%.*]] = mul nuw nsw i40 [[SWITCH_CAST]], 8
+; CHECK-NEXT: [[SWITCH_DOWNSHIFT:%.*]] = lshr i40 460303, [[SWITCH_SHIFTAMT]]
+; CHECK-NEXT: [[SWITCH_MASKED:%.*]] = trunc i40 [[SWITCH_DOWNSHIFT]] to i8
+; CHECK-NEXT: ret i8 [[SWITCH_MASKED]]
;
entry:
%rem = urem i64 %x, 5
>From 512c0b34e55176d7faf3708639c64d87cc7568d2 Mon Sep 17 00:00:00 2001
From: zhongyunde 00443407 <zhongyunde at huawei.com>
Date: Sat, 28 Oct 2023 02:52:19 -0400
Subject: [PATCH 2/2] [SimplifyCFG] Fix the compile crash when default branch
is unreachable
This modification will squash to the previous commit if accepted.
Seperate it just to make it more clearly to review.
---
llvm/lib/Transforms/Utils/SimplifyCFG.cpp | 6 +-
.../Transforms/SimplifyCFG/switch_mask.ll | 58 +++++++++++++++++++
2 files changed, 62 insertions(+), 2 deletions(-)
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 18187bcdedf0982..e79efd474de2747 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -6631,7 +6631,9 @@ static bool SwitchToLookupTable(SwitchInst *SI, IRBuilder<> &Builder,
BranchInst *RangeCheckBranch = nullptr;
// Grow the table to cover all possible index values to avoid the range check.
- if (UseSwitchConditionAsTableIndex) {
+ // It will use the default result to fill in the table hole later, so make
+ // sure it exist.
+ if (UseSwitchConditionAsTableIndex && HasDefaultResults) {
ConstantRange CR = computeConstantRange(TableIndex, /* ForSigned */ false);
// Grow the table shouldn't have any size impact by checking
// WouldFitInRegister.
@@ -6641,7 +6643,7 @@ static bool SwitchToLookupTable(SwitchInst *SI, IRBuilder<> &Builder,
return SwitchLookupTable::WouldFitInRegister(
DL, CR.getUpper().getLimitedValue(), KV.second /* ResultType */);
})) {
- // The default branch is unreachable when we enlarge the lookup table.
+ // The default branch is unreachable after we enlarge the lookup table.
// Adjust DefaultIsReachable to reuse code path.
TableSize = CR.getUpper().getZExtValue();
DefaultIsReachable = false;
diff --git a/llvm/test/Transforms/SimplifyCFG/switch_mask.ll b/llvm/test/Transforms/SimplifyCFG/switch_mask.ll
index 123519bc6921147..5e33769c8b25167 100644
--- a/llvm/test/Transforms/SimplifyCFG/switch_mask.ll
+++ b/llvm/test/Transforms/SimplifyCFG/switch_mask.ll
@@ -103,3 +103,61 @@ lor.end:
%0 = phi i8 [ 15, %sw.bb0 ], [ 6, %sw.bb1 ], [ 7, %sw.bb2 ], [ 0, %default ]
ret i8 %0
}
+
+; Negative test: The default branch is reachable, but has no result.
+define i1 @switch_lookup_with_small_i1_default_no_results(i32 %x) {
+; CHECK-LABEL: @switch_lookup_with_small_i1_default_no_results(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: [[AND:%.*]] = and i32 [[X:%.*]], 15
+; CHECK-NEXT: ret i1 false
+;
+entry:
+ %and = and i32 %x, 15
+ switch i32 %and, label %default [
+ i32 4, label %phi.end
+ i32 2, label %phi.end
+ i32 10, label %phi.end
+ i32 9, label %phi.end
+ i32 1, label %sw.bb1.i
+ i32 3, label %sw.bb1.i
+ i32 5, label %sw.bb1.i
+ i32 0, label %sw.bb1.i
+ i32 6, label %sw.bb1.i
+ i32 7, label %sw.bb1.i
+ i32 8, label %sw.bb1.i
+ ]
+
+sw.bb1.i: ; preds = %entry, %entry, %entry, %entry, %entry, %entry, %entry
+ br label %phi.end
+
+default: ; preds = %entry
+ unreachable
+
+phi.end: ; preds = %sw.bb1.i, %entry, %entry, %entry, %entry
+ %retval = phi i1 [ false, %sw.bb1.i ], [ false, %entry ], [ false, %entry ], [ false, %entry ], [ false, %entry ]
+ ret i1 %retval
+}
+
+; Negative test: The default branch is unreachable because all cases are listed.
+define i1 @switch_lookup_with_small_i1_unraachable(i64 %x) {
+; CHECK-LABEL: @switch_lookup_with_small_i1_unraachable(
+; CHECK-NEXT: entry:
+; CHECK-NEXT: [[REM:%.*]] = urem i64 [[X:%.*]], 3
+; CHECK-NEXT: ret i1 true
+;
+entry:
+ %rem = urem i64 %x, 3
+ switch i64 %rem, label %default [
+ i64 0, label %lor.end
+ i64 1, label %lor.end
+ i64 2, label %lor.end
+ ]
+
+default: ; preds = %entry
+ br label %lor.end
+
+lor.end: ; preds = %entry, %entry, %entry, %default
+ %0 = phi i1 [ true, %entry ], [ false, %default ], [ true, %entry ], [ true, %entry ]
+ ret i1 %0
+}
+
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