Reland "DAG: Preserve range metadata when load is narrowed" (#128144)

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -14957,12 +14957,37 @@ SDValue DAGCombiner::reduceLoadWidth(SDNode *N) {
   AddToWorklist(NewPtr.getNode());
 
   SDValue Load;
-  if (ExtType == ISD::NON_EXTLOAD)
-    Load = DAG.getLoad(VT, DL, LN0->getChain(), NewPtr,
-                       LN0->getPointerInfo().getWithOffset(PtrOff),
-                       LN0->getOriginalAlign(),
-                       LN0->getMemOperand()->getFlags(), LN0->getAAInfo());
-  else
+  if (ExtType == ISD::NON_EXTLOAD) {
+    const MDNode *OldRanges = LN0->getRanges();
+    const MDNode *NewRanges = nullptr;
+    // If LSBs are loaded and the truncated ConstantRange for the OldRanges
+    // metadata is not the full-set for the new width then create a NewRanges
+    // metadata for the truncated load
+    if (ShAmt == 0 && OldRanges) {
+      ConstantRange CR = getConstantRangeFromMetadata(*OldRanges);
+      unsigned BitSize = VT.getScalarSizeInBits();
+
+      // It is possible for an 8-bit extending load with 8-bit range
+      // metadata to be narrowed to an 8-bit load.  This guard is necessary to
+      // ensure that truncation is strictly smaller.
+      if (CR.getBitWidth() > BitSize) {
+        ConstantRange TruncatedCR = CR.truncate(BitSize);
+        if (!TruncatedCR.isFullSet()) {
+          Metadata *Bounds[2] = {
+              ConstantAsMetadata::get(
+                  ConstantInt::get(*DAG.getContext(), TruncatedCR.getLower())),
+              ConstantAsMetadata::get(
+                  ConstantInt::get(*DAG.getContext(), TruncatedCR.getUpper()))};
+          NewRanges = MDNode::get(*DAG.getContext(), Bounds);
+        }
+      } else if (CR.getBitWidth() == BitSize)
+        NewRanges = OldRanges;
+    }
+    Load = DAG.getLoad(
+        VT, DL, LN0->getChain(), NewPtr,
+        LN0->getPointerInfo().getWithOffset(PtrOff), LN0->getOriginalAlign(),
+        LN0->getMemOperand()->getFlags(), LN0->getAAInfo(), NewRanges);
+  } else
     Load = DAG.getExtLoad(ExtType, DL, VT, LN0->getChain(), NewPtr,
                           LN0->getPointerInfo().getWithOffset(PtrOff), ExtVT,
                           LN0->getOriginalAlign(),

llvm/test/CodeGen/AMDGPU/shl64_reduce.ll

@@ -13,23 +13,66 @@
 ; Test range with metadata
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
-; FIXME: This case should be reduced, but SelectionDAG::computeKnownBits() cannot
-;        determine the minimum from metadata in this case.  Match current results
-;        for now.
-
 define i64 @shl_metadata(i64 %arg0, ptr %arg1.ptr) {
 ; CHECK-LABEL: shl_metadata:
 ; CHECK:       ; %bb.0:
 ; CHECK-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
+; CHECK-NEXT:    flat_load_dword v1, v[2:3]
+; CHECK-NEXT:    s_waitcnt vmcnt(0) lgkmcnt(0)
+; CHECK-NEXT:    v_lshlrev_b32_e32 v1, v1, v0
+; CHECK-NEXT:    v_mov_b32_e32 v0, 0
+; CHECK-NEXT:    s_setpc_b64 s[30:31]
+  %shift.amt = load i64, ptr %arg1.ptr, !range !0, !noundef !{}
+  %shl = shl i64 %arg0, %shift.amt
+  ret i64 %shl
+}
+
+define i64 @shl_metadata_two_ranges(i64 %arg0, ptr %arg1.ptr) {
+; CHECK-LABEL: shl_metadata_two_ranges:
+; CHECK:       ; %bb.0:
+; CHECK-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
+; CHECK-NEXT:    flat_load_dword v1, v[2:3]
+; CHECK-NEXT:    s_waitcnt vmcnt(0) lgkmcnt(0)
+; CHECK-NEXT:    v_lshlrev_b32_e32 v1, v1, v0
+; CHECK-NEXT:    v_mov_b32_e32 v0, 0
+; CHECK-NEXT:    s_setpc_b64 s[30:31]
+  %shift.amt = load i64, ptr %arg1.ptr, !range !1, !noundef !{}
+  %shl = shl i64 %arg0, %shift.amt
+  ret i64 %shl
+}
+
+; Known minimum is too low.  Reduction must not be done.
+define i64 @shl_metadata_out_of_range(i64 %arg0, ptr %arg1.ptr) {
+; CHECK-LABEL: shl_metadata_out_of_range:
+; CHECK:       ; %bb.0:
+; CHECK-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
+; CHECK-NEXT:    flat_load_dword v2, v[2:3]
+; CHECK-NEXT:    s_waitcnt vmcnt(0) lgkmcnt(0)
+; CHECK-NEXT:    v_lshlrev_b64 v[0:1], v2, v[0:1]
+; CHECK-NEXT:    s_setpc_b64 s[30:31]
+  %shift.amt = load i64, ptr %arg1.ptr, !range !2, !noundef !{}
+  %shl = shl i64 %arg0, %shift.amt
+  ret i64 %shl
+}
+
+; Bounds cannot be truncated to i32 when load is narrowed to i32.
+; Reduction must not be done.
+; Bounds were chosen so that if bounds were truncated to i32 the
+; known minimum would be 32 and the shl would be erroneously reduced.
+define i64 @shl_metadata_cant_be_narrowed_to_i32(i64 %arg0, ptr %arg1.ptr) {
+; CHECK-LABEL: shl_metadata_cant_be_narrowed_to_i32:
+; CHECK:       ; %bb.0:
+; CHECK-NEXT:    s_waitcnt vmcnt(0) expcnt(0) lgkmcnt(0)
 ; CHECK-NEXT:    flat_load_dword v2, v[2:3]
 ; CHECK-NEXT:    s_waitcnt vmcnt(0) lgkmcnt(0)
 ; CHECK-NEXT:    v_lshlrev_b64 v[0:1], v2, v[0:1]
 ; CHECK-NEXT:    s_setpc_b64 s[30:31]
-  %shift.amt = load i64, ptr %arg1.ptr, !range !0
+  %shift.amt = load i64, ptr %arg1.ptr, !range !3, !noundef !{}
   %shl = shl i64 %arg0, %shift.amt
   ret i64 %shl
 }
 
+; FIXME: This case should be reduced
 define <2 x i64> @shl_v2_metadata(<2 x i64> %arg0, ptr %arg1.ptr) {
 ; CHECK-LABEL: shl_v2_metadata:
 ; CHECK:       ; %bb.0:
@@ -39,11 +82,12 @@ define <2 x i64> @shl_v2_metadata(<2 x i64> %arg0, ptr %arg1.ptr) {
 ; CHECK-NEXT:    v_lshlrev_b64 v[0:1], v4, v[0:1]
 ; CHECK-NEXT:    v_lshlrev_b64 v[2:3], v6, v[2:3]
 ; CHECK-NEXT:    s_setpc_b64 s[30:31]
-  %shift.amt = load <2 x i64>, ptr %arg1.ptr, !range !0
+  %shift.amt = load <2 x i64>, ptr %arg1.ptr, !range !0, !noundef !{}
   %shl = shl <2 x i64> %arg0, %shift.amt
   ret <2 x i64> %shl
 }
 
+; FIXME: This case should be reduced
 define <3 x i64> @shl_v3_metadata(<3 x i64> %arg0, ptr %arg1.ptr) {
 ; CHECK-LABEL: shl_v3_metadata:
 ; CHECK:       ; %bb.0:
@@ -55,11 +99,12 @@ define <3 x i64> @shl_v3_metadata(<3 x i64> %arg0, ptr %arg1.ptr) {
 ; CHECK-NEXT:    v_lshlrev_b64 v[0:1], v8, v[0:1]
 ; CHECK-NEXT:    v_lshlrev_b64 v[2:3], v10, v[2:3]
 ; CHECK-NEXT:    s_setpc_b64 s[30:31]
-  %shift.amt = load <3 x i64>, ptr %arg1.ptr, !range !0
+  %shift.amt = load <3 x i64>, ptr %arg1.ptr, !range !0, !noundef !{}
   %shl = shl <3 x i64> %arg0, %shift.amt
   ret <3 x i64> %shl
 }
 
+; FIXME: This case should be reduced
 define <4 x i64> @shl_v4_metadata(<4 x i64> %arg0, ptr %arg1.ptr) {
 ; CHECK-LABEL: shl_v4_metadata:
 ; CHECK:       ; %bb.0:
@@ -74,12 +119,15 @@ define <4 x i64> @shl_v4_metadata(<4 x i64> %arg0, ptr %arg1.ptr) {
 ; CHECK-NEXT:    v_lshlrev_b64 v[4:5], v13, v[4:5]
 ; CHECK-NEXT:    v_lshlrev_b64 v[6:7], v15, v[6:7]
 ; CHECK-NEXT:    s_setpc_b64 s[30:31]
-  %shift.amt = load <4 x i64>, ptr %arg1.ptr, !range !0
+  %shift.amt = load <4 x i64>, ptr %arg1.ptr, !range !0, !noundef !{}
   %shl = shl <4 x i64> %arg0, %shift.amt
   ret <4 x i64> %shl
 }
 
 !0 = !{i64 32, i64 64}
+!1 = !{i64 32, i64 38, i64 42, i64 48}
+!2 = !{i64 31, i64 38, i64 42, i64 48}
+!3 = !{i64 32, i64 38, i64 2147483680, i64 2147483681}
 
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 ; Test range with an "or X, 16"

llvm/test/CodeGen/X86/narrow-load-metadata.ll

@@ -0,0 +1,25 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 5
+; RUN: llc -mtriple=x86_64-unknown-linux-gnu < %s | FileCheck %s
+;
+; This test case is reduced from RangeConstraintManager.cpp in a ASan build.
+; It crashes reduceLoadWidth in DAGCombiner.cpp. Preservation of range
+; metadata must ensure that ConstantRange truncation is strictly smaller.
+
+define i8 @narrow_load_metadata(ptr %valptr) {
+; CHECK-LABEL: narrow_load_metadata:
+; CHECK:       # %bb.0: # %entry
+; CHECK-NEXT:    movzbl (%rdi), %eax
+; CHECK-NEXT:    movb %al, 4(%rdi)
+; CHECK-NEXT:    movl $0, (%rdi)
+; CHECK-NEXT:    retq
+entry:
+  %val = load i8, ptr %valptr, align 4, !range !0, !noundef !1
+  %retval.sroa.1.0.insert.ext.i = zext i8 %val to i64
+  %retval.sroa.1.0.insert.shift.i = shl i64 %retval.sroa.1.0.insert.ext.i, 32
+  %coerce.val.ii = trunc i64 %retval.sroa.1.0.insert.shift.i to i40
+  store i40 %coerce.val.ii, ptr %valptr, align 4
+  ret i8 %val
+}
+
+!0 = !{i8 0, i8 2}
+!1 = !{}