diff --git a/llvm/lib/MC/MCExpr.cpp b/llvm/lib/MC/MCExpr.cpp
--- a/llvm/lib/MC/MCExpr.cpp
+++ b/llvm/lib/MC/MCExpr.cpp
@@ -660,6 +660,18 @@
     // Try to find a constant displacement from FA to FB, add the displacement
     // between the offset in FA of SA and the offset in FB of SB.
     int64_t Displacement = SA.getOffset() - SB.getOffset();
+    bool Reverse = false;
+    if (FA == FB) {
+      Reverse = SA.getOffset() < SB.getOffset();
+    } else if (!isa<MCDummyFragment>(FA)) {
+      Reverse = std::find_if(std::next(FA->getIterator()), SecA.end(),
+                             [&](auto &I) { return &I == FB; }) != SecA.end();
+    }
+    if (Reverse) {
+      std::swap(FA, FB);
+      Displacement *= -1;
+    }
+
     bool Found = false;
     for (auto FI = FB->getIterator(), FE = SecA.end(); FI != FE; ++FI) {
       auto DF = dyn_cast<MCDataFragment>(FI);
@@ -678,13 +690,12 @@
         return;
       }
     }
-    // If FA is found or if FA is a dummy fragment not in the fragment list,
-    // (which means SA is a pending label (see flushPendingLabels)), we can
-    // resolve the difference.
-    if (Found || isa<MCDummyFragment>(FA)) {
-      Addend += Displacement;
-      FinalizeFolding();
-    }
+    // If the previous loop does not find FA, FA must be a dummy fragment not in
+    // the fragment list (which means SA is a pending label (see
+    // flushPendingLabels)). In either case, we can resolve the difference.
+    assert(Found || isa<MCDummyFragment>(FA));
+    Addend += Reverse ? -Displacement : Displacement;
+    FinalizeFolding();
   }
 }
 
diff --git a/llvm/test/MC/AArch64/arm64-small-data-fixups.s b/llvm/test/MC/AArch64/arm64-small-data-fixups.s
--- a/llvm/test/MC/AArch64/arm64-small-data-fixups.s
+++ b/llvm/test/MC/AArch64/arm64-small-data-fixups.s
@@ -2,6 +2,7 @@
 
 foo:
   .long 0
+  .p2align 2
 bar:
   .long 1
 
diff --git a/llvm/test/MC/ARM/directive-if-subtraction.s b/llvm/test/MC/ARM/directive-if-subtraction.s
--- a/llvm/test/MC/ARM/directive-if-subtraction.s
+++ b/llvm/test/MC/ARM/directive-if-subtraction.s
@@ -14,6 +14,16 @@
 orr r1, r1, #2
 .endif
 
+nop
+.arch_extension sec
+9997:nop
+.if 9997b - . == 0
+// ASM:    :[[#@LINE-1]]:5: error: expected absolute expression
+// DISASM: orr	r1, r1, #2
+orr r1, r1, #1
+.else
+orr r1, r1, #2
+.endif
 
 @ RUN: not llvm-mc -filetype=obj -triple arm-linux-gnueabihf --defsym=ERR=1 %s -o /dev/null 2>&1 | FileCheck --check-prefix=ARM-ERR %s
 @ RUN: not llvm-mc -filetype=obj -triple thumbv7a-linux-gnueabihf --defsym=ERR=1 %s -o /dev/null 2>&1 | FileCheck --check-prefix=THUMB2-ERR %s
diff --git a/llvm/test/MC/MachO/absolutize.s b/llvm/test/MC/MachO/absolutize.s
--- a/llvm/test/MC/MachO/absolutize.s
+++ b/llvm/test/MC/MachO/absolutize.s
@@ -94,7 +94,7 @@
 // CHECK:     Offset: 383
 // CHECK:     Alignment: 0
 // CHECK:     RelocationOffset: 0x1C4
-// CHECK:     RelocationCount: 3
+// CHECK:     RelocationCount: 1
 // CHECK:     Type: Regular (0x0)
 // CHECK:     Attributes [ (0x0)
 // CHECK:     ]
@@ -115,8 +115,6 @@
 // CHECK:   }
 // CHECK:   Section __data {
 // CHECK:     0x28 0 2 n/a GENERIC_RELOC_VANILLA 1 0x2B
-// CHECK:     0x10 0 2 n/a GENERIC_RELOC_LOCAL_SECTDIFF 1 0x2B
-// CHECK:     0x0 0 2 n/a GENERIC_RELOC_PAIR 1 0x2F
 // CHECK:   }
 // CHECK: ]
 // CHECK: Symbols [
diff --git a/llvm/test/MC/MachO/darwin-x86_64-reloc.s b/llvm/test/MC/MachO/darwin-x86_64-reloc.s
--- a/llvm/test/MC/MachO/darwin-x86_64-reloc.s
+++ b/llvm/test/MC/MachO/darwin-x86_64-reloc.s
@@ -176,20 +176,6 @@
 // CHECK-NEXT:       Symbol: _foo
 // CHECK-NEXT:     }
 // CHECK-NEXT:     Relocation {
-// CHECK-NEXT:       Offset: 0x9D
-// CHECK-NEXT:       PCRel: 0
-// CHECK-NEXT:       Length: 3
-// CHECK-NEXT:       Type: X86_64_RELOC_SUBTRACTOR (5)
-// CHECK-NEXT:       Symbol: _prev
-// CHECK-NEXT:     }
-// CHECK-NEXT:     Relocation {
-// CHECK-NEXT:       Offset: 0x9D
-// CHECK-NEXT:       PCRel: 0
-// CHECK-NEXT:       Length: 3
-// CHECK-NEXT:       Type: X86_64_RELOC_UNSIGNED (0)
-// CHECK-NEXT:       Symbol: _foo
-// CHECK-NEXT:     }
-// CHECK-NEXT:     Relocation {
 // CHECK-NEXT:       Offset: 0x95
 // CHECK-NEXT:       PCRel: 0
 // CHECK-NEXT:       Length: 3
@@ -239,48 +225,6 @@
 // CHECK-NEXT:       Symbol: _prev
 // CHECK-NEXT:     }
 // CHECK-NEXT:     Relocation {
-// CHECK-NEXT:       Offset: 0x55
-// CHECK-NEXT:       PCRel: 0
-// CHECK-NEXT:       Length: 2
-// CHECK-NEXT:       Type: X86_64_RELOC_SUBTRACTOR (5)
-// CHECK-NEXT:       Symbol: _bar
-// CHECK-NEXT:     }
-// CHECK-NEXT:     Relocation {
-// CHECK-NEXT:       Offset: 0x55
-// CHECK-NEXT:       PCRel: 0
-// CHECK-NEXT:       Length: 2
-// CHECK-NEXT:       Type: X86_64_RELOC_UNSIGNED (0)
-// CHECK-NEXT:       Symbol: _foo
-// CHECK-NEXT:     }
-// CHECK-NEXT:     Relocation {
-// CHECK-NEXT:       Offset: 0x4D
-// CHECK-NEXT:       PCRel: 0
-// CHECK-NEXT:       Length: 3
-// CHECK-NEXT:       Type: X86_64_RELOC_SUBTRACTOR (5)
-// CHECK-NEXT:       Symbol: _bar
-// CHECK-NEXT:     }
-// CHECK-NEXT:     Relocation {
-// CHECK-NEXT:       Offset: 0x4D
-// CHECK-NEXT:       PCRel: 0
-// CHECK-NEXT:       Length: 3
-// CHECK-NEXT:       Type: X86_64_RELOC_UNSIGNED (0)
-// CHECK-NEXT:       Symbol: _foo
-// CHECK-NEXT:     }
-// CHECK-NEXT:     Relocation {
-// CHECK-NEXT:       Offset: 0x45
-// CHECK-NEXT:       PCRel: 0
-// CHECK-NEXT:       Length: 3
-// CHECK-NEXT:       Type: X86_64_RELOC_SUBTRACTOR (5)
-// CHECK-NEXT:       Symbol: _bar
-// CHECK-NEXT:     }
-// CHECK-NEXT:     Relocation {
-// CHECK-NEXT:       Offset: 0x45
-// CHECK-NEXT:       PCRel: 0
-// CHECK-NEXT:       Length: 3
-// CHECK-NEXT:       Type: X86_64_RELOC_UNSIGNED (0)
-// CHECK-NEXT:       Symbol: _foo
-// CHECK-NEXT:     }
-// CHECK-NEXT:     Relocation {
 // CHECK-NEXT:       Offset: 0x3D
 // CHECK-NEXT:       PCRel: 0
 // CHECK-NEXT:       Length: 3
diff --git a/llvm/test/MC/MachO/reloc-diff.s b/llvm/test/MC/MachO/reloc-diff.s
--- a/llvm/test/MC/MachO/reloc-diff.s
+++ b/llvm/test/MC/MachO/reloc-diff.s
@@ -1,6 +1,7 @@
 // RUN: llvm-mc -triple i386-apple-darwin9 %s -filetype=obj -o - | llvm-readobj -r - | FileCheck %s
 
 _local_def:
+        .p2align 2
         .globl _external_def
 _external_def:
 Ltemp:
@@ -22,5 +23,9 @@
 // CHECK-NEXT:     0x0 0 2 n/a GENERIC_RELOC_PAIR 1 0x0
 // CHECK-NEXT:     0x8 0 2 n/a GENERIC_RELOC_LOCAL_SECTDIFF 1 0x0
 // CHECK-NEXT:     0x0 0 2 n/a GENERIC_RELOC_PAIR 1 0x0
+// CHECK-NEXT:     0x4 0 2 n/a GENERIC_RELOC_LOCAL_SECTDIFF 1 0x0
+// CHECK-NEXT:     0x0 0 2 n/a GENERIC_RELOC_PAIR 1 0x0
+// CHECK-NEXT:     0x0 0 2 n/a GENERIC_RELOC_SECTDIFF 1 0x0
+// CHECK-NEXT:     0x0 0 2 n/a GENERIC_RELOC_PAIR 1 0x0
 // CHECK-NEXT:   }
 // CHECK-NEXT: ]